Feasibility demonstration for HLW disposal

W
Document Sample
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							  35  2004
Bulletin
      Technical-scientific contributions on the topic of nuclear waste management




                                                                                   Feasibility demonstration for HLW disposal
      4                                                                            The Opalinus Clay Project – motivation and results

      12                                                                           Geological background

      24                                                                           Concept for facilities and operation of a deep geological repository

      34                                                                           Analysis and demonstration of long-term safety
Impressum                                                                                                                                        Contents   Demonstration of disposal feasibility for high-level waste
                    nagra Bulletin no. 35                                                                                                                   The Opalinus Clay Project – motivation
                    May 2004                                                                                                                     4          and results
                                                                                                                                                            The demonstration of feasibility of disposing
                    Editorial, text                                                                                                                         of spent fuel (SF), high-level waste (HLW) and long-
                    Dr. Meinrad Ammann                                                                                                                      lived intermediate-level waste (ILW) requested by
                    Dr. Emil Kowalski                                                                                                                       the authorities is based on the Opalinus Clay Project
                    Andreas L. Nold                                                                                                                         in the Zürcher Weinland region.
                    The content of this issue was compiled from the three
                    main reports of the Opalinus Clay Project (see p. 8).

                    Concept, layout and graphics                                                                                                            Geological background
                    Franca Moser                                                                                                                 12         The aim of the investigations was to determine
                    David McKie                                                                                                                             whether the Opalinus Clay in the Zürcher Weinland
                    Dr. Meinrad Ammann                                                                                                                      fulfils the requirements placed on the environment
                                                                                                                                                            for a deep geological repository (siting demonstration).
                    Translation                                                                                                                             The data serve as a basis for assessing engineering
                    Linda McKinley                                                                                                                          feasibility and for analysing the long-term safety of the
                                                                                                                                                            repository.
                    Publisher
                    Nagra
                    National Cooperative for the                                                                                                            Concept for facilities and operation
                    Disposal of Radioactive Waste                                                                                                24         of a deep geological repository
                    Hardstrasse 73, CH-5430 Wettingen                                                                                                       The facilities and operation concept is used
                    Telephone 056-437 11 11                                                                                                                 to demonstrate the feasibility of constructing a deep
                    Fax 056-437 12 07                                                                                                                       geological repository. The individual components
                    E-mail info@nagra.ch                                                                                                                    of the facility form a modular construction system
                    Internet www.nagra.ch                                                                                                                   termed the “Reference Project” and serve as the
                                                                                                                                                            basis for the safety demonstration.
                    nagra Bulletin appears in German and English.
                    The text may be reproduced in part or in whole pro-
                    vided the source is acknowledged. Use of photo-                                                                                         Analysis and demonstration
                    graphs requires the permission of the relevant                                                                               34         of long-term safety
                    agency.                                                                                                                                 A system of multiple safety barriers ensures the
                                                                                                                                                            long-term containment of the spent fuel and radioac-
                    nagra Bulletin is available free of charge                                                                                              tive waste. The effectiveness of the overall
                    from Nagra, either individually or by subscription.                                                                                     system and compliance with the protection objectives
                                                                                                                                                            specified by the safety authorities are demonstrated
                    Photographs p. 3, 4, 12, 24, 34: Armeefilmdienst,                   Title of this issue                                                  by safety analyses.
                    Comet, DesAir, Nagra, Prisma.                                      If spent fuel from nuclear power plants is not
                                                                                       reprocessed but is disposed of directly in a deep
                                                                                       geological repository, the re-usable fissile materi-
                                                                                       als in the fuel are treated as waste. The title of this
                                                                                       bulletin “Feasibility demonstration for HLW dis-
                    Cover image                                                        posal“ therefore also includes spent fuel elements
                    A Leioceras opalinum fossil was found in the centre of a           in the case where they are not reprocessed but
                    drillcore from the Benken borehole. This ammonite occurs           disposed of directly.
                    frequently in the Opalinus Clay and gave the rock its name.        Long-lived intermediate-level waste will also be
                    The fact that the fossil, which is around 180 million years old,   disposed of in the repository for spent fuel and
                    is so well preserved is evidence of the excellent isolation        high-level waste.
                    capacity of the Opalinus Clay. (Picture: Comet, Zürich)



nagra Bulletin 35
2                                                                                                                                                                                                                        3
                                                                                                                                                                                                                            Summary

                                                                                                                                                                                                                            With the Opalinus Clay Project
                                                                                                                                                                                                                            reports, Nagra has presented a
                                                                                                                                                                                                                            demonstration of the feasibility
                                                                                                                                                                                                                            of waste disposal to the federal
                                                                                                                                                                                                                            government. The Project docu-
                                                                                                                                                                                                                            ments how and where, in Swit-
                                                                                                                                                                                                                            zerland, a safe geological repos-
                                                                                                                                                                                                                            itory can be constructed for spent
                                                                                                                                                                                                                            fuel (SF), high-level waste (HLW)
                                                                                                                                                                                                                            and long-lived intermediate-level
                                                                                                                                                                                                                            waste (ILW). This article provides
                                                                                                                                                                                                                            an overview of the Project and
                                                                                                                                                                                                                            its results.


                                                                                                                          Reproduziert mit Bewilligung von swisstopo (BA046047)




                                      Demonstration of disposal feasibility for high-level waste


    The Opalinus Clay Project                                                                                                                                                     Following a series of studies on the     the SF/HLW/ILW repository con-




     – motivation and results
                                                                                                                                                                                  waste management concept, engi- centrated on the region of Northern               “Entsorgungsnachweis“ – demon-
                                                                                                                                                                                  neering studies and field and labora- Switzerland. At the time, the focus          stration of disposal feasibility
                                                                                                                                                                                                                                                                    The “Entsorgungsnachweis“ consists
                                                                                                                                                                                  tory investigations, Nagra submitted was on the crystalline basement as a         of three fundamental elements:
                                                                                                                                                                                  Project Gewähr to the federal govern- potential host rock, given the wealth
                                                                                                                                                                                                                                                                    Siting demonstration
                                                                                                                                                                                  ment at the beginning of 1985 [Lit. 1] . of information available both inter-     Demonstration that one or more
                                                                                                                                                                                  The waste management concept nationally and specifically on the                    disposal sites with suitable geologi-
                    Introduction and motiva-                 Government Ruling of 6th October for this feasibility study was Nagra                                                assumed two repositories – one for region of Northern Switzerland.                cal and hydrogeological properties
                                                                                                                                                                                                                                                                    can be found in Switzerland.
                    tion behind the Project                  1978 on the Atomic Act (1959) – the National Cooperative for the                                                     spent fuel (SF), vitrified high-level Based on reviews and evaluations of
                    In terms of responsibility towards       required the waste producers to Disposal of Radioactive Waste.                                                       waste (HLW) and long-lived inter- the project by its safety authorities,          Demonstration of
                    man and the environment, it is           prepare a project that offered an assur-                                                                             mediate-level waste (ILW) and one        the Federal Council released its deci-   engineering feasibility
                                                                                                                                                                                                                                                                    Demonstration that a repository can
                    incumbent upon our society to pro-       ance of the safe, long-term manage-                                                                                  for low- and intermediate-level waste    sion on Project Gewähr on 3rd June       be constructed and operated at such
                    vide for the safe, long-term disposal    ment and disposal of radioactive waste.                                                                              (L/ILW). A model site was identified 1988. The key findings were as fol-            a site using current technology.
                    of radioactive wastes arising from the   The resulting feasibility demonstra-                                                                                 for each facility, with representative   lows:
                                                                                                                                                                                                                                                                    Safety demonstration
                    production of nuclear energy and         tion – entitled Project Gewähr                                                                                       properties that could be expected • All aspects of the feasibility dem-           Demonstration that a repository
                    from use of radioactive materials in     (guarantee) – showed how deep                                                                                        based on actual geological investiga-       onstration for L/ILW were ac-         fulfils the requirements set by the
                    medicine, industry and research          geological repositories [1] that met the                                                                             tions. Because of the tectonic stabil-      cepted.                               authorities with respect to long-term
                                                                                                                                                                                                                                                                    safety.
                    (Fig. 1); this requirement is anchored   requirements of the safety authorities [1] The new Nuclear Energy Law uses the term                                  ity of the area and its low seismic • The safety demonstration for SF/
                    in Swiss legislation. The Federal        could be constructed. Responsible “deep geological repository”.                                                      activity, Nagra’s investigations for        HLW/ILW was also accepted, but


nagra Bulletin 35

4                                                                                                                                                                                                                                                                                                           5
                                                                                                                     the article on page 12 on the geo-
                                                                                                                     logical background to the project)
                                                                                                                                                                  ����������������������������������������������������������
                                                                                                                     led to selection of the Opalinus Clay
                  Figure 1
      Today, radioactive
                                                                                                                     in the Zürcher Weinland region.                                                        ����                                                     ����                                               ����                       ����                         ����

 waste is being held in                                                                                              The process of narrowing down the
         interim storage.




                                                                                                                                                                                                                                                                            ������������������
                                                                                                                     possibilities was broadly conceived;




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   Between the nuclear
                                                                                                                     it was followed closely by the federal




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       power plants and




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       Zwilag AG (in the                                                                                             authorities and is documented trans-




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         picture), there is                                                                                          parently in a series of interim reports




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                                                                                                                                                                                                                                                                                                                                                                                                                                                  �����������������������
  sufficient capacity to




                                                                                                                                                                                                                                                                                                                                                       ����������������������
                                                                                                                     (see text-box on page 15).
    store all radioactive
                                                                                                                     An important reason for including




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  waste and spent fuel




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                                                                                                                                                                                                ���������������
arising from the opera-                                                                                              sedimentary formations in the evalu-
       tion of the power                                                                                             ation of disposal options was that the




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                    plants.




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                                                                                                                     spatial predictability of the forma-




                                                                                                                                                                                                                                                                                                                                   ����
                                                                                                                     tions was expected to be good. In
                                                                                                                     terms of lithology and mineralogy,
                                                                                                                     the Opalinus Clay is a homogeneous
                                                                                                                                                                                                                                                                                                                               ����������������������                                                                                                                         �����������
                                                                                                                     formation with uniform deposition
                                                                                                                                                                                                                                                               ��������                                                                    ���������                                                                                                                        ����������
                                                                                                                     conditions over large parts of North-                                                                                                     ����������                                                                  ������
                                                                                                          Comet
                                                                                                                     ern Switzerland. This ensures good
                                                                                                                     transferability of parameters meas-
                                                                                                                                                                                               ������������������                                                                        ��������������������������                                                    ������������������������
                                                                                                                     ured at other locations (e.g. in the
                                                                                                                     Mont Terri Rock Laboratory) to the
                                                                                                                     investigation area in the Zürcher         Figure 2
                                                                                                                     Weinland. The geometric boundaries        Key steps on the way to realising a deep geological repository for spent fuel (SF), vitrified high-level waste (HLW) and long-lived
                                                                                                                     of the Opalinus Clay layer in the         intermediate-level waste (ILW). The Opalinus Clay Project documents the priority option of disposal in sedimentary rock. The
                                                                                                                                                               option of disposal in the crystalline basement was presented in detail in Project Gewähr 1985 [Lit. 1] and in more detail in later
                                                                                                                     Weinland, with its simple structure       Nagra reports [Lit. 2, 3, 5] .
                                                                                                                     and tectonic stability, are well known
                                                                       Targeted studies in sedi-                     thanks to a 3D seismic survey carried
                                  not the siting demonstration, i.e.   mentary formations                            out in the area. This also meant that
                                  that a suitable rock body of suffi-   The feasibility demonstration repre-          rock parameters measured locally in
                                  cient extent could be found at a     sents an important interim step on            an exploratory borehole could be          repository (see article on page 24)
                                  concrete site in Switzerland.        the way to realising a geological             extrapolated over the entire investiga-   assume a disposal concept as out-                                                                                                 The Law confirms the principle that long-term safety should be inde-
                                                                                                                                                                                                                                                                                                 pendent of human activity and hence the concept of deep geological
                              • Engineering feasibility was dem-       repository for a particular category          tion area. It was shown that the rock     lined in the new Nuclear Energy Law
                                                                                                                                                                                                                                                                                                 disposal. However, the demands of society are also taken into account
                                  onstrated for all waste types.       of waste. The procedure followed for          in the area investigated in the Zürcher   (see text-box on the right). The                                                                                                  in that the decision to definitively close the repository, which is seen
                              • The nuclear power plant operators      SF/HLW/ILW is shown schemati-                 Weinland fulfils all the basic require-    engineering project comes to the                                                                                                  as irreversible, is made only after an extended phase of monitoring.
                                  were directed to continue their      cally in Figure 2. Besides a final            ments for the geological environment      conclusion that, in the Opalinus                                                                                                  This concept of “monitored long-term geological disposal“[Lit. 4] which
                                                                                                                                                                                                                                                                                                 is based on the studies of the EKRA (Expert Group on Disposal Concepts
                                  work on radioactive waste disposal   synthesis of the results for the crystal-     of a deep repository.                     Clay of the Zürcher Weinland, a                                                                                                   for Radioactive Waste) working group, foresees a geological repository
                                  and to extend research associated    line basement [Lit. 2, 3] , the decision of   The large lateral extent of the Opali-    geological repository for SF/HLW/                                                                                                 that will be closed only after an extended monitoring phase.
                                  with disposal of HLW/ILW to          the Federal Council in 1988 led               nus Clay layer and its constant thick-    ILW can be constructed, operated,
                                  include sedimentary formations.      Nagra to intensify its studies of sedi-       ness in the potential siting area offer   monitored and, if necessary, closed
                               This latter requirement provided the    ments in Northern Switzerland; the            a considerable degree of flexibility in    within a few years in accordance
                               direct impetus for systematic inves-    outcome of this was the Opalinus              terms of placing the underground          with legal requirements using present-
                               tigation of sedimentary rocks in        Clay Project discussed here (Fig. 3).         facilities. These will occupy only        day technology. The requirements
                               Switzerland and the selection of a      The systematic evaluation of options          around one-tenth of the area assessed     relating to monitoring and control
                               preferred investigation area based on   in terms of sedimentary rocks and             as being most suitable. Investigations    can be fulfilled and retrievability of
                               safety considerations.                  potential areas where they occur (see         of the engineering feasibility of the     the waste is also assured.


nagra Bulletin 35

6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        7
                                                                                                                                                    Evaluation of                            account and alternative release sce-        and the potential siting area in
                                                                                                                                                    long-term safety                         narios are calculated. In addition, a       the Zürcher Weinland.
                                                                                                                                                    The decisive step on the way to          series of “what if?” cases are intro-    The federal authorities subjected the
                                                                                                                                                     demonstrating the secure, long-term     duced; these consider phenomena          Project to an international review by
                                                                                                                                                     disposal of waste is to demonstrate     that are outside the range of effects    the NEA/OECD in 2003 [Lit. 10] . The
                                                                                                                                                     long-term safety for an underground     and processes to be expected scien-      detailed evaluation of the documen-
                                                                                                                                                     facility that can be constructed using  tifically but could compromise the        tation during 2003 and 2004 will
                                                                                                                                                     existing technology, based on avail-    functioning of the safety barriers. In   be completed in 2005 with a report
                                                                                                                                                     able geological information. The        this way it can be checked whether       to the Federal Council (see Fig. 4).
                                                                                                                                                     extensive investigations carried out    the system will also withstand unex-     A broad public consultation proce-
                                                                                                                                                     come to the conclusion that, for all    pected developments.                     dure under the lead of the federal
                                                                                                                                                     realistically conceivable scenarios of                                           government is then foreseen, with a
                                                                                                                                                     the future evolution of the disposal Conclusions and request                     decision by the Federal Council at
                                                                                                                                                     system, the potentially resulting to the federal government                      the beginning of 2006.
                                                                                                                                                     radiological dose to the population Besides demonstrating the feasibility
                                                                                                                                                     will be below strict quantitative       and safety of deep geological dis-       Outlook
                                                                                                                                                     limits set by the safety authorities of posal of SF/HLW/ILW in Switzer-          The next step on the way to realising
                                                                                                                                                     the federal government in Guideline     land, the Entsorgungsnachweis will       a repository is to prepare for an appli-
                                                                                                                                                     R-21[Lit. 6] (see article on page 34 of also serve as a basis for the decision   cation for a general licence, which
                                                                                                                                                     this Bulletin).                         of the Federal Council on future         will specify the future site (see long-
                                                                                                                                                    The waste is isolated from the           procedure to be followed in the          term scheme in Fig. 4). In addition
                                                                                                                                                     human environment by a system of HLW programme. The Opalinus                     to technical aspects, social and eco-
                                                                                                                                                     multiple safety barriers. The major- Clay Project also provides the back-        nomic impacts have to be investi-
                                                                                                                                                     ity of the radioactivity will decay ground for planning future waste             gated and an environmental impact
                                                                                                                                                     during the time when the waste          management activities, including         study carried out. The layout and
                                                                                                                                                     containers are still intact and thus    estimation of costs. The Project         location of the different facilities will
                                                                                                                                                     ensure complete containment. Even       should also provide the framework        have to be discussed with the siting
                                                                                                                                                     after this, the radioactive substances  for in-depth social dialogue on          region. Only then can an application
                                                                                                                                                     will be contained by the bentonite      waste management issues.                 for a general licence be submitted.
                                                                                                                                                     and host rock barriers, i.e. they will Based on the results of the Opalinus      The Nuclear Energy Law states that
                                                                                                                                                     continue to decay within the dis- Clay Project and the systematically            the siting Canton and immediately
                                                                                                                                                     posal system. The retention mecha- conducted selection procedure,                neighbouring Cantons and countries
                                                                                                                                                     nisms in the host rock ensure that Nagra has requested the Federal               have to be involved in preparing the
                                                                                                                                                     the distribution of the remaining Council                                        decision on the general licence. A
                                                                                                                                                     radionuclides into the environment • to acknowledge that the condi-              public inspection period is also fore-
                                                                                                                                                    – for example by diffusion and dis-         tions attached to Project Gewähr      seen. The decision of the Federal
                                                                                                                                                     persion – occurs so slowly and is          1985 by the government evalua-        Council on the licence application
                                                                                                                                                     spatially so diluted that the nuclide      tion of 3rd June 1988 have been       has to be submitted to the Federal
                    Nagra




                                                                                                                                                     concentration is always negligibly         fulfilled and to confirm that the       Assembly for approval; this decision
                                                                                                                                                     low.                                       feasibility of disposal has been      is then subject to an optional national
                            Figure 3
                                                                                                                                                    These qualitative statements were           demonstrated                          referendum (popular vote).
                            Many Nagra employees and around 30 external research institutes and technical contractors contributed to the Opalinus
                            Clay Project. The three main reports [Lit. 7, 8, 9] have been published and are also available on Nagra‘s website.       derived from quantitative safety • to agree to focusing future inves-
                                                                                                                                                     analyses carried out for a series of       tigations associated with deep
                                                                                                                                                     release scenarios. Besides the most        geological disposal of spent fuel,
                                                                                                                                                     likely evolution of the disposal           vitrified high-level waste and long-
                                                                                                                                                     system, all deviations that can be         lived intermediate-level waste in
                                                                                                                                                     realistically assumed are taken into       Switzerland on the Opalinus Clay


nagra Bulletin 35

8                                                                                                                                                                                                                                                                                 9
                                                                                                                                               Step by step towards our goal             Literature references
                             ���������������������������������������������������������������                                                   Following the political decision on       1
                                                                                                                                                                                             Nagra (1985): Report series on Project Gewähr. Nagra
                                                                                                                                                                                             Project Reports NGB 85-01 to 85-08 (NGB 85-09 overview
                             ��������������                                                                                                    the general licence, it is planned to         in English). Nagra, Wettingen.
                                                                                                                                               construct an underground rock labo-
                                                                                                                                                                                         2
                                                                                                                                                                                             Nagra (1994): “Kristallin-I. Safety Assessment Report“;
                                                                                                                                                                                             Nagra Technical Report NTB 93-22. Nagra, Wettingen.
                                                              ������������������������������������������
                                                              �������������������������������������������������
                                                                                                                                               ratory at the future site. This will      3
                                                                                                                                                                                             Nagra (1994): “Kristallin-I. Conclusions from the regional
                                                                                                                                                                                             investigation programme for siting a HLW repository in
                             �����������������������������               ������������                                                          allow data to be acquired for support-        the crystalline basement of Northern Switzerland“; Nagra
                             �����������������                           ������������������                     ����������������������������
                                                                                                                                               ing the application for the repository        Technical Report NTB 93-09E. Nagra, Wettingen.
                                                                                                                                                                                         4
                                                                                                                                                                                             EKRA (2000): “Disposal Concepts for Radioactive Waste“;
                             ����������������������                      �������������������                                                   construction licence. Objections to           Expert Group on Disposal Concepts for Radioactive Waste
                                                                                                                                                                                             (EKRA).
                                                                                                                                               permits for exploratory work can be       5
                                                                                                                                                                                             Thury M., Gautschi A., Mazurek M., Müller W.H., Naef H.,
                                                                                                                                               lodged in independent courts.                 Pearson F.J., Vomvoris S. and Wilson W. (1994): “Geology and
                                                                                                                                                                                             Hydrogeology of the Crystalline Basement of Northern
                                                             ������������������������������������������������                                  Construction and later operation of           Switzerland. Synthesis of Regional Investigations 1981
                                                                                                                                                                                            – 1993 within the Nagra Radioactive Waste Disposal
                                                                                                                                               the repository also require to be             Programme“; Nagra Technical Report NTB 93-01. Nagra,
                                                                                                                ���������������������������
                             �������������������������                                                                                                                                       Wettingen.
                             ���������������������������������           ������������������������������         �������������������� ����      licensed. Based on the current esti-          HSK/KSA (1993): “Guideline for Swiss Nuclear Installa-
                                                                                                                ���������������������                                                    6

                                                                                                                                               mation, the start of operation is             tions HSK-R-21/e: Protection Objectives for the Disposal
                                                                                                                                                                                             of Radioactive Waste“; Swiss Federal Nuclear Safety
                                                                                                                                               foreseen for the period 2040 to 2050          Inspectorate (HSK), Federal Commission for the Safety of
                                                                                                                                               (Fig. 4). Up till the decision on con-        Nuclear Installations (KSA). HSK, Villigen.
                                                                                                                                                                                         7
                                                                                                                                                                                             Nagra (2002): “Projekt Opalinuston: Konzept für die
                                               ������������������������������������������������������������������������                        struction is made, multinational              Anlage und den Betrieb eines geologischen Tiefenlagers.
                                                                                   ��
                                                                ��������������������������������������                                                                                       Entsorgungsnachweis für abgebrannte Brennelemente,
                                                                        ����������������������                                                 solutions will also remain open n             verglaste hochaktive sowie langlebige mittelaktive
                                                                           �����������������                                                                                                 Abfälle“; Nagra Technical Report NTB 02-02. Nagra, Wet-
                                                                                                                                                                                             tingen.
                                                                                                                                                                                         8
                                                                                                                                                                                             Nagra (2002): “Projekt Opalinuston: Synthese der geowis-
                                                                            �������������������������                                                                                        senschaftlichen Untersuchungsergebnisse. Entsorgung-
                                                                 ���������������������������������������������������                                                                         snachweis für abgebrannte Brennelemente, verglaste
                                                                                                                                                                                             hochaktive Abfälle sowie langlebige mittelaktive Abfälle“;
                                                                         ��������������������������������                                                                                    Nagra Technical Report NTB 02-03. Nagra, Wettingen.
                             �������������������������                   ������������������������������         ���������������������������                                              9
                                                                                                                                                                                             Nagra (2002): “Project Opalinus Clay: Safety report.
                                                                         �������������������������                                                                                           Demonstration of disposal of spent fuel, vitrified high-
                                                                                                                                                                                             level waste and long-lived intermediate-level waste
                                                                         �������������������                    ��������������������                                                         (Entsorgungsnachweis)“; Nagra Technical Report NTB
                                                                         ��������������                         ��������                                                                     02-05. Nagra, Wettingen.
                                                                                                                                                                                         10
                                                                                                                                                                                             Nagra (2002): “Safety of Disposal of Spent Fuel, HLW and
                                                                                                                                                                                             Long-lived ILW in Switzerland. An International Peer
                                                                                                                                                                                             Review of the Post-closure Radiological Safety Assessment
                                                                                                                                                                                             for Disposal in the Opalinus Clay of the Zürcher Wein-
                                                                                                                                                                                             land“; Nuclear Energy Agency (Organisation for Economic
                                                                    ������������������������������������������
                                                                                                                                                                                             Co-operation and Development), Issy-les-Moulineaux,
                                                                           �����������������������������
                                                                                                                                                                                             France.



                                                                        �������������������������������

                             �������������������������                   �������������
                                                                         ������������������                     ���������������������
                                                                         �����������������������                ���������������������
                                                                         ������������������




                                                                          ����������������������������
                Figure 4                                                 �������������
                             �������������������������
           There are still                                               ������������������                     ��������������������
 numerous steps to be                                                    �����������������������                ����������������������            This issue of “nagra Bulletin“
   taken before a deep                                                   ������������������
                                                                                                                                                  summarises the content of the
 geological repository                                                                                                                            three main reports of the
    can be constructed                                                                                                                            Opalinus Clay Project [Lit. 7, 8, 9]
     and operated. The                                                                                                                            (see Fig. 3) on the geological
 right of the people to                                                                                                                           background, the concept for
be involved is ensured                                                    ����������������������������                                            facilities and operation and
  by law in the case of                                                                                                                           the analysis of long-term
   all decisions and the                                                                                                                          safety of a deep repository.
   granting of licences.


nagra Bulletin 35

10                                                                                                                                                                                                                                                          11
                                                                                                                                                                                                                                                                    Summary

                                                                                                                                                                                                                                                                    The geological and hydrogeo-
                                                                                                                                                                                                                                                                    logical situation is decisive in
                                                                                                                                                                                                                                                                    evaluating the long-term safety
                                                                                                                                                                                                                                                                    of a repository constructed at a
                                                                                                                                                                                                                                                                    particular site. Selection of a
                                                                                                                                                                                                                                                                    potential disposal site and its
                                                                                                                                                                                                                                                                    detailed characterisation there-
                                                                                                                                                                                                                                                                    fore have to proceed carefully.
                                                                                                                                                                                                                                                                    This article provides an overview
                                                                                                                                                                                                                                                                    of the geological investigations
                                                                                                                                                                                                                                                                    carried out and the evaluation
                                                                                                                                                                                                                                                                    of their results.
                                     Demonstration of disposal feasibility for high-level waste



      Geological background
                                                                                                                                              The geological and hydrogeological           that formed the basis for Project             this respect. The procedure evolved
                                                                                                                                              situation in and around the reposi-          Gewähr 1985 [Lit. 2] . As part of the         with the approval of the safety
                    Introduction                                                                                                              tory thus has great significance in           sediment programme, which was                 authorities of the federal government
                    The guiding principle behind radio- ate-level waste, geological disposal           tems, thus reducing radionuclide       assessing the long-term safety of the        intensified from 1987, Nagra carried           and their appointed experts (see also
                    active waste disposal strategies is to    has emerged internationally as the       release.                               facility. A great deal of care has to        out a broadly based, transparent              text-box on page 15).
                    ensure effective isolation of radio- best strategy for dealing with these •        Retardation of radionuclide trans-     be taken in selecting the potential          evaluation and narrowing-down                 In a first step, Nagra published a
                    toxic waste substances from the           materials. The timescales involved in    port, for example by sorption or       repository site and in its detailed          procedure (see Figs. 1, 2), leading to        comprehensive study[Lit. 3] on poten-
                    human environment. This is in con- geological processes are incomparably           colloid filtration, resulting in       characterisation.                            identification of potential sedimen-           tially suitable sedimentary rocks (see
                    trast with the approach of disposal by longer than those of the often short-       decay of the nuclides before they                                                   tary host rocks and potential siting          Fig. 2 top). This study was based on
                    dilution to harmless concentrations, lived societal structures that would          are potentially released into the      Selection and characterisa-                  areas. This procedure, which was              extensive geological literature, as
                    as is practised, for example, in intro- otherwise be required for monitored        biosphere.                             tion of the siting region                    monitored closely by the safety               well as on the results of Nagra’s own
                    ducing waste gases from burning of waste storage. The geological barriers •        Protection of the engineered con-      Following a comprehensive evalua-            authorities, was documented in three          investigations and those of third
                    fossil fuels into the atmosphere. fulfil several functions:                         tainment barriers from climatic        tion of the host rock options that           Nagra Technical Reports [Lit. 3, 4, 5] . In   parties (thematic regional studies;
                    Because of the long isolation times • Containment of the waste materi-             influences (e.g. glacial erosion) and   came into question [Lit. 1] , the crystal-   the process of narrowing-down, the            deep boreholes and 2D seismics; cf.
                    required in the case of spent fuel, high-    als at locations where there are no   from inadvertent human intru-          line basement initially emerged into         better option was always selected,            Fig. 1). This work revealed a priority
                    level waste and long-lived intermedi-        significant water-conducting sys-      sion.                                  the forefront of the investigations          with safety criteria being decisive in        for clay-rich rock layers, namely the


nagra Bulletin 35

12                                                                                                                                                                                                                                                                                                  13
                                                                                                                                                                                                                                                                                            Opinion of the German expert
                                                  ������������������������                                                                                   �����������������������������������������������                                                                                group AkEnd
                                                         �����
                      �����                                                                                                                                                                                                                                                                  At the request of the German-
                                                         �����
                                  ������                                                                                                                                                                                                                                                     Swiss Commission for the
                                                                                                                                                                                                                                                                  �����                      Safety of Nuclear Installations,
                                                                                                                                                            �������          ���������        �����                            ��������
                      ����                                                                                                                                                                                                                                        ����������                 the site selection procedure in
                                                                                                                                                            ������           �����            ������                           ����
                                                                                                                                                                                                                                               �����              �������
                                                                                                                                                            ���������        ����������       ����������                       ����������                                                    Switzerland was examined
                                                                                                                                                                                                              ��������                         ����������         ����������
                                                                                                                                                            ��������         ��������         ��������        ����             ��������        �������            ��������                   closely by the German group
                                                                          ��������������                                                                                                                                                       �����                                         “Arbeitskreis Auswahlver-
                                   �����
                                                                                                                                                                                                              ����������
                                                                            �����                                                                                                                                                              ����������                                    fahren Endlagerstandor te
                                                ������                      �����
       ������                                                                                                                                                                                                                                                                                (AkEnd)“. The group came to
                                   ����
                                                                                                                                                                                                                                                                                             the conclusion[Lit. 10] that, on the
                                                                                                                                                                                                                                            ������������                                     whole, the Swiss selection
                                                                                                                                                                                                                                            �������������
                                                                                                            Figure 1                                                                                                                        ��������                                         procedure fulfilled the require-
                                                            �����                                                                                                                                                                                                                            ments placed internationally
                                                                                                            The procedure of identifying a potential
                                                                                                            siting area was based on a large                                                                                                ������������         ��������������              on such a site selection process.
                                                                                                                                                                                                                                            ������������������   ���                         The selection of the Zürcher
                                                                                                            number of results from boreholes and
                    ������                                                                                                                                                                                                                                                                   Weinland as the preferred
                                                                                                            seismic campaigns. The availability of a
                                                                                                            comprehensive database meant that                                                                                                       �������������������������                option for a SF/HLW/ILW repos-
                                                                                                            the narrowing-down procedure started                                                                                                    �����������������                        itory, made on the basis of
                                                                                                                                                                                                                                                    �����������������������                  safety considerations, was
                                                                                                            from a broad basis.
                                                                                                                                                                                                                                                                 �������������               considered by the group to be
                                                                                                                                                                                                                                                                 �������                     justified. The politically moti-
                                                                                                                                                                                                                                                                                             vated accusation that the Wein-
                                                                                                                                                                                                                                                                                             land was selected because of
                                                                                                                                                                                                                                                                                             its proximity to the German
                                                                                                                                                                                                                                                                                             border was dismissed.
                       Opalinus Clay and the Lower Fresh-         The selection of the priority area for    location of the area and its geological
                       water Molasse formations. Potential        local exploration was considered by       profiles. Thanks to the comprehen-                                                                                                                   Figure 2
                                                                                                                                                               Various rock and siting area options were evaluated as part of the sediment programme. The broadly
                       siting regions for further investiga-      the authorities to be geologically        sive understanding of the area and
                                                                                                                                                             conceived, transparent narrowing-down procedure was closely supervised by the safety authorities and
                       tion were identified for these two          transparent and justified. The fed-        the homogeneous lithology of the                     led, after several steps, to selection of the Opalinus Clay in the region of the Zürcher Weinland. The
                       options.                                   eral government’s experts also            Opalinus Clay, parameters measured                                                       details of the procedure are documented in several reports [Lit. 3, 4, 5] .
                       In the following phase (1990 to            approved the investigation concept        at other locations can be reliably
                       1993), the selection was further nar-      proposed by Nagra for the Opalinus        transferred to the situation in the
                       rowed down (Figs. 2, 3). The Lower         Clay. The main components of the          Zürcher Weinland (see Fig. 6). Local                                          ������������
                                                                                                                                                                                          �����������������
                       Freshwater Molasse, with its large         investigation programme were:             differences in boundary conditions
                                                                                                                                                                                               �����������������������������������������������������
                       spatial potential but restrictions in     • A 3D seismic campaign in the             that are not dependent on rock type                        Figure 3                ���������������������������
                       terms of explorability, was classified         Zürcher Weinland covering an           (e.g. differing overburden of the host               Options in the                                                                                                                                   �������
                                                                                                                                                                                               ���������������������������������
                       as a reserve option. In 1994, the             area of around 50 km 2 [Lit. 6, 7] .   rock, different stress regime) were            sediments Opalinus                  ������������������
                                                                                                                                                                Clay and Lower                                                                                                                            ������������
                       Opalinus Clay was identified as the        • An exploratory borehole in the           taken into account when transfer-             Freshwater Molasse,
                       first-priority sedimentary host rock           community of Benken [Lit. 8] .         ring data.                                        with the Zürcher            ��������������������                                               ������
                                                                                                                                                                                                                                                                                         �����
                                                                                                                                                            Weinland region as                                                                                                �����                                       ��������
                       option and the northern part of the       • Experiments in the Opalinus Clay                                                                                           ����������������������������������������������
                                                                                                                                                               the first-priority                                                                                                         �����                            ��������
                       Zürcher Weinland as the preferred             as part of the international re-       Have basic requirements                         Opalinus Clay area.
                                                                                                                                                                                              �����������������������������                                                                                      ������




                                                                                                                                                                                                                                                                                                                                  ����
                                                                                                                                                                                                                                                             ����������������
                                                                                                            been fulfilled?                                                                    �����������������������������




                                                                                                                                                                                                                                                                                                      ��
                       area for site-specific investigations.         search programme being con-                                                           The areas “Jurasüd-                                                                               ����������     ��
                                                                                                                                                                                                                                                                               ��




                                                                                                                                                                                                                                                                                                          ��
                                                                                                                                                                                              ��������������������




                                                                                                                                                                                                                                                                                                          �
                       The selection criteria were:                  ducted at the Mont Terri Rock          The analysis of the investigation               fuss-Bözberg“ and                                                                                                ���������
                      • Simple geologica l structures                Laboratory (Canton Jura) [Lit. 9] .    results [Lit. 11] shows that the selected   “Nördlich Lägeren“ for
                                                                                                                                                         the Opalinus Clay and                                                                   ���������                                       ������
                           (Tabular Jura)                        • Comparative regional studies of          area in the Zürcher Weinland fulfils               the entire Lower                                                                                              ����
                      • Tectonically quiet, low seismicity           Opalinus Clay, as well as com-         the basic requirements placed on a             Freshwater Molasse




                                                                                                                                                                                                                                                                              ����
                      • Opalinus Clay at a depth between             parisons with clay deposits being      siting area for a deep geological                  area are reserve                                                                                  ��������
                                                                                                                                                          options. Also shown                                                             �������
                           400 to 900 metres                         studied in other countries with a      repository[Lit. 12]. Specific aspects are      are the investigation                                                                                                                                           �����
                      • Large area without any indication            view to geological disposal.           discussed in detail in the following          areas for the crystal-                                                                                                           �������
                                                                                                                                                                                                                                                                                          ���������
                           of tectonic deformation                Figures 4 and 5 show the geographic       sections. Firstly, however, the most                line basement.



nagra Bulletin 35

14                                                                                                                                                                                                                                                                                                                                       15
                                                                                                                                                                          has a very low hydraulic conductivity
                                                                                                                                           �����                                                                      ����������������������������������
                                                                                                                                                        ��
                                                                                                                                                             ��
                                                                                                                                                                          and provides a stable geochemical
                               ����������������������                                                                                                          ���
                                                                                               ������������                                                           �   environment with favourable condi-          ���������������




                                                                                                                                                                                                                                                                        ��
                                                                                                �
                                                                                                ��                                                                                                                    ������                                                           ������������
                                                                                             ��                                                                           tions for radionuclide retention and




                                                                                                                                                                                                                                                              ���������
                                                                                                                                                                                                                                                             �����������
                                                                                           �




                                                                                                              ��
                                                                                        ��
                                                                                    ���                                         ��
                                                                                                                                                                          the long-term functioning of the
                                                                                                                                                                                                                                         ��������
                                                                               ����
                                                                          ���                                                                                                                                                      ��������          ����
                                                                     ����                                                                                                 engineered barriers. Given its rock
                                                                                                           �                                          ����
                                                                                                     ���� �                                                               mechanical properties, there would
                                                                                                         �




                                                                                                                            ��
                                                                                                                                                                                                                                                                                                        ����
                                                                                                                                      ����                                be no reason to call into question the
                                                                                                                                 ����                                                                                    �����
                 Figure 4                                                                                                    ��                                           feasibility of constructing a deep                                                                                       ���������
                                                                                                                           ��
                                                                                                                       ���                                                                                                                                                                          ������




                                                                                                                                ���




                                                                                                                                                                                                                                                                                                                                                            Nagra
    Geological overview                                                                                             ��                                                    repository. The fact that there are                                          ����������
                                                                                                                ����                                                                                                                                                            ���������




                                                                                                                                   �
    map of the Opalinus                                �                      ���                             ��
      Clay investigation                        ������                           ��                      �                                                                generally low permeability forma-
                                         ����
                                                                                       �
                                    ����
                                                                ��




  area and its surround-          ��                                                                                                                    �����             tions above and below the host rock                                                                      �������
                              ���
                                                                     ��




                                            ����
                                                                         ���




                    ings.                                                                    ������                                                                       enhances the containment func-
                                                                            ��




                                                                                                                                                                                                                                                                       ������
                                                                                                                                                                          tion.                                                                     ����
                                       ���������������������������������                                                 ���������������������������������
                                       ��������������������                                                              ���������������
                                       ����������������������������
                                       �������������������                                                               �������������������                              Sufficient extent of the host
                                                                                                                                                                          rock body                                              ����                                                 �������    ��������
                                                                                                                                                                                                                                                                             �������� ��������   ������   �����
                                                                                                                                                                          Because of its almost constant thick-                                                                                                     Figure 6
                                                                                                                                                                                                                                                           ������                                                   Around 180 million years ago, the sea covered large areas of
                             important properties are summa-                                           significantly deformed. It is also in a                             ness, lateral extent and lithological
                                                                                                                                                                                                                                                                                                                    what is now the European mainland. In the area Strasbourg-
                             rised as follows:                                                         seismically quiet area of Switzerland,                             continuity, the Opalinus Clay offers                                                                                                      Stuttgart-Zürich-Bern, silts and muds were deposited in the sea
                                                                                                       with a low uplift and erosion rate.                                a large element of flexibility in terms      ��������������������    ������������
                                                                                                                                                                                                                                                                                                                    and, over the course of time, solidified to form a clay layer
                                                                                                                                                                                                                                                                                 �����        �������������������
                             Long-term geological stability                                                                                                               of placing a repository. The slight         ������������                                                                                  (Opalinus Clay), which has consistent properties over a large
                                                                                                                                                                                                                                                                                                                    area.
                             The investigation area is located at                                      Good host rock properties                                          dip of the host rock unit allows the                                                                                                      Small photograph: Underground, the Opalinus Clay is a hard
                             the edge of the region influenced by                                       The Opalinus Clay host rock in the                                 depth of the facility to be selected                                                                                                      rock, as shown by this large drillcore from the Mont Terri Rock
                             the Alps; tectonically, it is subject to                                  investigation area is sufficiently thick                            and optimised to meet requirements.                                                                                                       Laboratory. In clay-pits at the surface, it is often friable or
                                                                                                                                                                                                                                                                                                                    loamy due to weathering influences.
                             a slight compressive stress but is not                                    and has a homogeneous lithology. It                                The situation is presented in Figure 7.



    ��                                                                                                                                                       ��             ����������
                                                                         ���������������
 ����������
              ����             ���������                      ����                                    ������                         ���������
                                                                                                                                                                            �     ��������������������              The area required for the under-                     Robustness in the event of                 either remain restricted to the imme-
 ���                 �����                                                                                                                                        ���       �������������
                                                                                                               ��                            ��                             �     ������������������������
                                                                                                                                                                                                                    ground facilities is around two                      perturbations                              diate tunnel vicinity or do not sig-
    �                                                                                                                                                             �         �     ��������������������              square kilometres. Based on the                      The selection of a low permeability        nificantly compromise the long-term
                                                                                                                                                                            �     ������������������������
 ����                                                                                                                                                             ����                                              results of the investigations, a total               host rock in a tectonically slightly       isolation capacity of the host rock.
                                                                                                                                                                            ��������
                     ����                                                                                                                                                                                           area of 35 square kilometres is avail-               compressive and seismically quiet          The absence of workable natural
�����                                                                                                                                                             �����     �     �������������������������
                                                           ����������������������������                                                                                     �     ����������������������            able for placing the repository. To                  setting, as well as a disposal depth       resources also makes it unlikely that,
                                                                                                                                                                            �     ���������������������
                                                                                                                                                                            �     �������������
                                                                                                                                                                                                                    ensure optimum protection from                       several hundred metres underground,        in the future, there will be any con-
     ��                                 ���������������                                                                                                      ��             �     ����                              long-term erosion, however, the area                 offer optimum protection from con-         flict of use or inadvertent human
 ���������� ��������                   ������                              ���������                      ���������                           ����������������              �     ������
 ��� �����                                                                                                                                                    ���                                                   to the north of the Wildensbuch                      ceivable perturbations (e. g. due to       intrusion into the facility.
                                                                                                                                                                            �     �����������������
                                                                                                                                                                            �     ��������������������������        flexure – where the overburden is less                glaciation events, movement along
    �                                                                                                                                                             �
                                           ��                                                                                                                               �     �������������
                                                                                                                                                                                                                    than 600 metres – is not taken into                  fault zones, earthquake effects). The      Explorability
 ����                                                                                                                                                             ����      ��������
                     ����                                                                                                                                                   �     ���������������������������       consideration. The remaining 22                      self-sealing capacity of the host rock     The simple geological structure,
�����                                                                                                                                                             �����     �     ���������������
                                                                                                                                                                                                                    square kilometres represent an area                  and the stable geochemical condi-          together with the tectonically slightly
                                  �����������������������������                                                                                                             �     ����������������������������
                                                                                                                                                                            �     �����������                       more than ten times that actually                    tions have the result that perturba-       disturbed sub-horizontal bedding
                                                                                                                                                                            �     �����                             required. Within this area, a dis-                   tions due to the presence of the           and the flat topography, ensure good
 Figure 5                                                                                                                                                                   �     ��������������
                                                                                                                                                                                                                    posal zone of eight square kilometres                repository itself (excavation disturbed    explorability of the geometric condi-
 Geological profiles through the Zürcher Weinland 3D seismic investigation area along the lines SW-NE and NW-                                                                ���   �������������������
 SE from Figure 4. The Benken borehole is located at the intersection of the profile lines.                                                                                  ���   ���������������                   has been identified as being of first                  zone, release of corrosion and degra-      tions (high resolution 3D seismics).
                                                                                                                                                                                                                    priority.                                            dation gases, chemical alterations)        The homogeneity of the host rock


 nagra Bulletin 35

 16                                                                                                                                                                                                                                                                                                                                                                                   17
��������������������������������������������������������������������                                                                                      and its low lithological variability      future evolution of the host rock in
                         ���                          ���                                 ���                       ���
                                                                                                                                                          result in properties that are spatially   its geological surroundings can thus
                                                                                                              �����������������������������               more or less constant. This allows        be predicted plausibly over the time
                                                                                                              ���������������������                       lithological information from the         period relevant for evaluating long-
                                                                                                              � �������������������
 ���
                                                                                                              ���������������������
                                                                                                                                                          Benken borehole to be extrapolated        term safety (one million years) and                                                                                               Figure 8
                                                                                                              �� ����������������������                   over the investigation area.              beyond.                                                                                                                           Opalinus Clay under
                                                            ��
                                                              �
                                                                                                              � ������������������                                                                                                                                                                                                    the scanning electron
                                                                                        ��                                                                                                                                                                                                                                            microscope. The
                                                                                                                                                                                                    The geosphere as a radio-
                                                                         ���




                                                                                                                                                          Predictability                                                                                                                                                              sample consists of clay
                                                                                                                                                          The geological evolution of the           nuclide barrier                                                                                                                   minerals which have
                                                                                 ���




 ���                                                                                                                                                      investigation area is well known and       To evaluate the functioning of the                                                                                               associated to form
                                                                                                                                                                                                                                                                                                                                      sheet-like aggregates.
                                                                                                                                                          is based on a large number of inde-        geosphere as a transport barrier, it is
                                                                                             �               ���
                                                                                                                                                                                                                                                                                                                                      In the centre is a
                                                                                        ��
                                                                                                                                                          pendent qualitative and quantitative       necessary to take into account the                                                                                               feldspar mineral.
                                                                                                 ���




                                                                           ��                                                                             arguments. Because of this situation,      hydraulic parameters as well as dif-
                                                                                                                                                          and not least because of the simple        fusion and sorption in the rock. It
                                                                                                 ���




                                                                                                                          �
                                                       ������                     ���                                 ��
                                                                                                                                                          geological structure of the area, the      was shown that:
                                                                                                               �
                                                                                                             ��




 ���

                                                      ��������                                                                                            range of different geological evolu-      • The dominant transport process
                                                                                                                                    ���


                                                                                                                                                          tion scenarios is very limited. The             is diffusion; advection plays
                                                                                                                                                                                                          either a secondary role, or none
                                                                                                                                    �
                                                                                                                                ��




                                                                                                                                                                                                          at all.
                                                                                                                                                                                                                                                                                                                    2 µm
 ���
                                                                                                                                                                                                    • Fault zones in the Opalinus Clay
                                                                                                                              ���              ���             ���            ���                         do not represent preferential
                            �
                          ��
                                         ��                                          ��                      ���
                                                                                                                                                                                                          flowpaths.                                                                                                     H.-R. Bläsi
                                     �
                                  ��
                                                                                                                   ���                                                  ���������������������
                                               ���
                                                                                                                                                                                                    • Stable, reducing geochemical
                                                                  ��
                                                                    �
                                                                                                       ��
                                                                                                         �                                                             ��������������������
                                                                         ���                                                                                                                              conditions prevail.
 ���
                                                                                                                                                          ��                                         The key to understanding the prop-        Hydraulic conductivity of faults            hydraulic conductivities shows that
                                                                           ���


                                                                                                                   ���
                                                                                                                                                                                                     erties of the Opalinus Clay is its        All investigations in boreholes and         diffusion is the dominant transport
                                                                                                                                                                                                     microstructure (Fig. 8). Given its        tunnels in the Opalinus Clay indicate       process. An additional argument
                                                                                                                                                                                                     porosity of around twelve volume          that the hydraulic conductivity of any      supporting this is the arcuate distri-
                                                                                                                                                     ��                                              percent, the rock contains a signifi-      fault zones present does not differ         bution of the concentrations of
                       ����        ����              ����                        �
                                                                                                                   ���                                                                               cant component of water but,              from that of the intact rock, provided      numerous elements, which is typical
 ���
                                                                                                                                                                                                     because of the pronounced filigree         the overburden is at least 200 metres.      for diffusion processes, as well as the
                                                                                                                                                                                                     structure of the pore space, the          This can be explained by the self-seal-     isotope ratios in the porewater (see
��������������������������������������������������                                                                                                                                                   porewater and dissolved substances        ing capacity of the Opalinus Clay.          Fig. 10). In the case of the Benken
                                                                                                                   ���                                                                               are practically immobile.                 Self-sealing processes were also iden-      borehole, the diffusion profile affects
           �����������������������                     ��              ���������������                                                                                                               Figure 9 shows the profi le of the         tified in in-situ experiments in the         not only the Opalinus Clay but also
           �����                                                                                                                                               ��
                                                       ��              �������������������                                                ��                                        ���              Benken exploratory borehole. The          Mont Terri Rock Laboratory [Lit. 9, 11] .   the layers both above and below the
     ���
           ��������������������������                  ��              ������������������������                                                                                  ���������
     ���
           ���������������������������������
                                                       ��              ������������������������                                                                                          �           characterisation of the Opalinus          The absence of mineral veins and            formation. This illustrates that dif-
           ���������������������������������                                                                       ���
                                                                                                                                                                                                     Clay gives values for hydraulic con-      alterations is evidence that, in the        fusion is also the dominant transport
           �����������������
           �������������                                                                                                                                                                             ductivity that show little scatter,       geological past, there were no signifi-      process in a significant part of the
           ����������������������                                                                                                                                                                    typically in the range 2 . 10 -14 to      cant rock-water interactions or sig-        confining units. Between the host
           ���������������������                                                                                               ������                                                    ��
           �������������
                                                                                                                               ��������                                                              1 . 10- 13 metres per second. Hydrau-     nificant water f low through the            rock and the regional aquifers
                                                                                                                   ���
                                                                                                                                                                                                     lic overpressures were measured in        Opalinus Clay.                              (Malm above, Muschelkalk below),
           �������
                                                                                                                                                                                                     the Opalinus Clay; these can be                                                       there are generally low permeability
Figure 7                                                                                                                                                                                             interpreted as relicts of the subsid-     Diffusion as the dominant                   clayey and evaporitic rocks over the
Structural map showing the depth contours of the 3D seismic investigation area (isohypses centre host rock). The contours show that the strata dip towards
                                                                                                                                                                                                     ence history or as being due to the       transport mechanism                         entire investigation area. The inter-
the south-east. The area that is potentially suitable for construction of the underground facility is shown in green (explanation in box top right).
The insert (bottom right) shows the layer inclination (with the regional dip towards the south-east subtracted). In the potentially suitable area, the only                                          compressive tectonic stress, which is     A comparison of the diffusion con-          calated sandy, limy or dolomitic
large structural element is the Wildensbuch flexure, which has been ruled out for the construction of emplacement tunnels.                                                                            oriented more or less north-south.        stants for the host rock with the low       layers represent partly water-bearing


nagra Bulletin 35

18                                                                                                                                                                                                                                                                                                                                                         19
                                                                                                                                                     strata, but they are generally only a      ated and reinforced by the swelling                                                                                                                              Figure 10
 �����         ������                                                                                             ����������
 ���           ���
                                 �����������������                   ��������������
                                                                                                                  ������������                       few metres thick and isolated from         of the bentonite. In its final condi-                                   ���������������������������������������������                                             Measured data for
                                                                                           ����������������                     �����
                                                                                                                                                                                                                                                                                                                                                                 deuterium (δ2H) in
                                                                                                                                                     one another. The confining units            tion, the excavation disturbed zone                                                                                                                              ground- and porewa-
                                                                  ��� � ���                            ���         �� ���   �� ���   �� ��   �� ��                                                                                                               ���
                                                                                                                                                     therefore cause additional radionu-        is expected to behave again as a                                                                                                                ����             ters from the Benken
      ���
     ����                      ��������������������                                                                                                  clide retardation.                         homogeneous porous medium with                                   ���         ����������������                                                                    borehole obtained

                                                                   ���������������
     ����                      �������������������
                                                                                                                                                                                                                                                                             �������������������                                                                 using a range of
                                                                                                                                                                                                a slightly enhanced porosity com-                                ���         ������������                                                       ����������
      ����                     ����                                                                                                                                                                                                                                                                                                             �������          methods. The arcuate




                                                                                                                                                                                                                                            ������������������
      ����                                                                                                                                            Stable geochemical conditions             pared to the intact rock. It will also                           ���                                                                            ������           distribution can be
                                                                                                                                                     The porewater in the Opalinus Clay         have an effective axial permeability                                                                                                                             explained only by
                                                                                                                                                                                                                                                                 ���                                                                                             diffusive exchange
                               ����������������
                                                                                                                                                     – originally sea-water – changed           that is still an order of magnitude                                                                                                             �������������
                               �������
                                                                                                                                                                                                                                                                 ���
                                                                                                                                                                                                                                                                                                                                                ������������     (arrows) between
                                                                                                                                                      composition during the subsidence,        above that of the intact rock. Hydro-                                                                                                           ���������        ground- and porewa-
                                                                                                                                                                                                                                                                                                                                                ��������������
     �����                     �����������������
                                                                                                                                                      compaction and uplift of the Opali-       geological model calculations have                               ���                                                                                             ters and excludes
     �����
                                                                                                                                                      nus Clay over a period of 180 million     shown that, even if the permeability                                                                                                            ����             substantial vertical
                               ������������                                                                                                                                                                                                                      ���                                                  ����������
                                                                                                                                                                                                                                                                                                                      ��������                                   advective water flow.
     �����
                                                                                                                                                      years. Today, it has a salinity around    of the excavation disturbed zone is                                                                                                             ������           Model calculations
                                                                                                                                                                                                                                                                 ���
                                                                                                                                                      one-third that of sea-water. The          significantly higher, water f low                                  ���          ���        ���        ���         ���          ���                               (dashed lines) show
                               �����������������������                                                                                                                                                                                                                                                ��������������                                             that it has taken
     �����                                                                                                                                            composition is determined to a large      through the repository will not be
                                                                                                                                                                                                                                                                                                                                                                 around 0.5 million
                                                                                                                                                      extent by chemical equilibria with        significantly increased because it is
                                                                                                                                                                                                                                                                       ���������������������������          �
                                                                                                                                                                                                                                                                                                              �������������������������������                    years for the observed
     �����
     �����
                               �������������������                                                                                                    the rock (particularly with clay min-     dependent primarily on the perme-                                      ������������������������
                                                                                                                                                                                                                                                                                                            �
                                                                                                                                                                                                                                                                                                              ����������������������������������������������     deuterium distribution
                                                                                                                                                                                                                                                                                                            �����������������������������������������
                               ����������������������                                                                                                 erals and carbonates). The concen-        ability of the intact host rock.                                                 ������������������                                                              to be established.
                                                                                     ���                                                                                                                                                                                         �����������������
 ������
                               �������������                                                                                                          tration of mobile components that                                                                                          ���������������

 ������
                               �������������
                               ��������������������
                                                                                                                                                      are independent of the rock compo-        Geochemical alterations
 ������
 ������
 ������                        �������������������������������                                                                                        sition (mainly anions) changes very       The geochemical alterations in the
                               ������������
                               ������������������                                                                                                     slowly and only to a restricted extent,   tunnel surroundings (primarily             mum of two years). Once the repos-                                     spans. On the long term, such an
 ������
                               ������������������������
                                                                                                                                                      because diffusion is the dominant         pyrite oxidation) during the con-          itory has been closed, interaction                                     alteration zone could extend to a
 ������
                               ����������������                  ���                                                                                  solute transport process. Overall, the    struction and operational phase of a       with cement mortar leads to forma-                                     maximum of a few metres. The for-
 ������
                                                                                                                                                      geochemical conditions are very           repository are negligible due to the       tion of highly alkaline porewaters in                                  mation of new minerals would be
                               �������������                                                                  �                                       stable and reducing.                      fact that the tunnels remain open for      the ILW tunnels; these can react with                                  expected to reduce the porosity and
                                                                                                                                                                                                only a short period of time (maxi-         the Opalinus Clay over long time                                       increase the sorption capacity. The
 ������
                               �����������������
                                                                                                       �                                             Effects of the repository                                                                                                                                    geochemical changes in the tunnel
 ������
                               ���������������                                                                                                       on the geosphere                                                                                                                                             vicinity thus have no negative impact
 ������                        ����
 ������                        �������������                                                                                                         Excavation disturbed zone                                                                                                                                    on radionuclide retention.
 ������
 ������                        ����������������������������
 ������                        ����������������������������
                                                                                     ���                                                             During tunnel construction, stress
                               ����������
                                                                                                                                                     changes lead to formation of an                                                                                                                              Heat production from the waste
                                                                                                   �                                                 excavation disturbed zone around                                                                                                                             As the SF/HLW will generate heat
 ������                        �����������
 ������
                               �������������������
                                                                                     ���                                                             the cavities (Fig. 11). The influence                                                                                                                         over several thousand years, the
 ������                                                                                                                                              of this zone on the host rock and its                                                                                                                        effect of the heat pulse on the host
                               ����������������
 ������                                                                                                                                              barrier function is, however, very                                                                                                                           rock was investigated. The reposi-
 ������
                               ���������������                                                                                                       restricted in terms of time and space.                                                                                                                       tory layout and the initial tempera-
 ������                        ����������������
 ������
 ������
                                                                                                                                                     The permeability of the excavation                                                                                                                           tures of the waste to be emplaced
                               �������������                                                                                                         disturbed zone during the construc-
 ������
 ������                        �������������                                                                                                         tion and operational phase is several
                               ���������������������
 �������
                                                                                                                                                     orders of magnitude higher than that
             �������������������������                           ��������������������������������������               � ���������
                                                                                                                                                     of the undisturbed host rock. Once
                                                                                                                                                     the repository has been closed, the
                                                                                                                                                     excavation disturbed zone and the
Figure 9                                                                                                                                                                                                                                                                                 B. Niederberger
                                                                                                                                                     bentonite and cement backfills re-            Figure 11
Benken borehole: lithological profile with hydraulic conductivities and heads obtained from packer tests
                                                                                                                                                                                                  Stress-induced fissures in the excavation disturbed zone of a tunnel in the
(vertical red bars) and long-term monitoring (blue points). The horizontal bars show the uncertainty band-                                           saturate and self-sealing of the dis-
                                                                                                                                                                                                  Mont Terri Rock Laboratory.
widths.                                                                                                                                              turbed zone occurs; this is acceler-


nagra Bulletin 35

20                                                                                                                                                                                                                                                                                                                                                                                   21
                           were defined in such a way that the            Gas production                              water flow in the host rock. Even if           shown that a significant increase in      vides a sound basis for evaluating the   Literature references
                           maximum temperature at the tunnel             In a deep repository, corrosion and         pessimistic assumptions are made,             the hydraulic conductivity of indi-      protective and barrier functions of      1
                                                                                                                                                                                                                                                        VSE, GKBP, UeW and Nagra (1978): “Konzept für die
                                                                                                                                                                                                                                                        nukleare Entsorgung in der Schweiz“; Verband
                           wall after around 1000 years will be          degradation gases are produced by           the potential increase in water flow           vidual faults in the Opalinus Clay       the geosphere over very long time           Schweizerischer Elektrizitätswerke (VSE), Gruppe
                           approximately 95 degrees Celsius.             the waste and the containers. Diffu-        will not exceed one order of magni-           occurs only when the overburden is       spans.                                      der Kernkraftwerkbetreiber u. -Projektanten (GKBP),
                                                                                                                                                                                                                                                        Konferenz der Überlandwerke (UeW), Nagra.
                           The mineralogical effects of such a           sion and advection processes are not        tude. Under such circumstances,               less than 200 metres. Future glacier     Remaining uncertainties are small.       2
                                                                                                                                                                                                                                                        Nagra (1985): Report series on Project Gewähr. Nagra
                                                                                                                                                                                                                                                        Project Reports NGB 85-01 to 85-08 (NGB 85-09
                           temperature increase can be consid-           efficient enough to remove all gener-        diffusion remains the dominant                advances will follow the valley net-     However, in order to take them into         overview in English). Nagra, Wettingen.
                           ered negligible as the Opalinus Clay          ated gases in solution and migration        transport process.                            work that exists today. Their “sur-      account, the safety analysis consid-
                                                                                                                                                                                                                                                     3
                                                                                                                                                                                                                                                        Nagra (1989): “Sediment study – Intermediate report
                                                                                                                                                                                                                                                        1988: Disposal options for long lived radioactive
                           was exposed to similarly high tem-            thus occurs as a gas phase preferen-                                                      face” erosion will keep pace with        ered band-widths or pessimistic             waste in Swiss sedimentary formations. Executive
                                                                                                                                                                                                                                                        summary“; Nagra Technical Report NTB 88-25E.
                           peratures (up to 85 °C) over much             tially along the bedding of the intact      Long-term geological                          uplift and will thus be of the same      alternative values in addition to           Nagra, Wettingen.
                           longer time periods during its subsid-        host rock, the excavation disturbed         evolution                                     order as linear erosion. The lateral     reference parameters for almost all
                                                                                                                                                                                                                                                     4
                                                                                                                                                                                                                                                        Nagra (1991): “Sedimentstudie – Zwischenbericht
                                                                                                                                                                                                                                                        1990: Zusammenfassende Übersicht der Arbeiten
                           ence history. Besides thermal stresses,       zone or along existing fault zones via      The long-term geological evolution            hill ranges will remain largely          the aspects treated; in some cases,         von 1988 bis 1990 und Konzept für das weitere
                                                                                                                                                                                                                                                        Vorgehen“; Nagra Technical Report NTB 91-19.
                           the temperature increase will result          classic two-phase f low or micro-           was considered over a time span of            intact and glacial scouring will be      alternative conceptual models were          Nagra, Wettingen.
                           in a porewater overpressure and a             scopic fissure formation. For the gas        around one million years. Evolution           restricted to already existing over-     also prepared. The effects of the
                                                                                                                                                                                                                                                     5
                                                                                                                                                                                                                                                        Nagra (1994): “Sedimentstudie – Zwischenbericht
                                                                                                                                                                                                                                                        1993: Zusammenfassende Übersicht der Arbeiten
                           reduction in the mechanical strength          generation rates expected in the tun-       over such a time period can be esti-          deepened channels.                       uncertainties are evaluated as part of      von 1990 bis 1994 und Konzept für weitere Untersu-
                                                                                                                                                                                                                                                        chungen“; Nagra Technical Report NTB 94-10. Nagra,
                           of the host rock. As the emplacement          nels, the formation of large-scale          mated plausibly on the basis of                                                        the safety analysis (see article on         Wettingen.
                           tunnels will already be backfilled by          macroscopic tension joints can be           detailed analysis of the geological           Evaluation of existing                   page 34). As a result, it can be dem-
                                                                                                                                                                                                                                                     6
                                                                                                                                                                                                                                                        Birkhäuser Ph., Roth Ph., Meier B. and Naef H. (2001):
                                                                                                                                                                                                                                                       “3D-Seismik: Räumliche Erkundung der mesozoischen
                           this point, this will not lead to any         ruled out. The formation of gas can         past. Predictions beyond this are             information                              onstrated with sufficient certainty          Sedimentschichten im Zürcher Weinland“; Nagra
                                                                                                                                                                                                                                                        Technical Report NTB 00-03. Nagra, Wettingen.
                           significant increase in the size of the        lead to overpressures in the emplace-       possible [Lit. 11], but contain an increas-   The understanding of the geological      that the overall geological situation    7
                                                                                                                                                                                                                                                        Nagra (2000): “3D Seismics in the Zürcher Weinland“;
                           excavation disturbed zone.                    ment tunnels, which could influence          ing element of uncertainty.                   conditions in the investigation area     in the investigation area, including       “nagra Bulletin“ No. 33. Nagra, Wettingen.
                                                                                                                                                                                                                                                     8
                                                                                                                                                                                                                                                        Nagra (2001): “Sondierbohrung Benken – Untersu-
                                                                                                                     The Zürcher Weinland belongs to               is very good, for several different      the host rock properties, fulfils the        chungsbericht (Text- und Beilagenband)“; Nagra
                                                                                                                                                                                                                                                        Technical Report NTB 00-01. Nagra, Wettingen.
                                                                                                                     one of the seismically most quiet             reasons: the high quality of the 2D      requirements placed on a potential       9
                                                                                                                                                                                                                                                        Thury M. (2002): “The Mont Terri Rock Laboratory.
                                                                                                                     areas of Switzerland, but still lies in       and 3D seismic campaigns, the            siting area. There is no geoscientific       Overview of the ongoing programme“; “nagra
                                                                                                                                                                                                                                                        Bulletin“ No. 34, pages 24-35. Nagra, Wettingen.
                                                                                                                     the outermost boundary zone of the            general homogeneity of the host rock     evidence that would, in principle,       10
                                                                                                                                                                                                                                                        AkEnd (2002): “Stellungnahme zum Auswahlverfah-
                                                                                                                                                                                                                                                        ren Opalinuston im Zürcher Weinland“; Arbeitskreis
     ������������������������������������������                                                                      foreland, which is subject to slight          without any signif icant lateral         call into question the construction         Auswahlverfahren Endlagerstandorte (AKEnd),
                                                                                                                     compressive stress due to alpine              change in rock composition, the          and safety of a deep geological             Federal Ministry for the Environment, Nature Con-
                                                                                                                                                                                                                                                        servation and Nuclear Safety (BMU), Berlin/Bonn.
     �������������                                                                                                   crustal shortening. This manifests            cored and intensively tested Benken      repository in the Zürcher Wein-          11
                                                                                                                                                                                                                                                        Nagra (2002): “Projekt Opalinuston: Synthese der
                                                                                                                                                                                                                                                        geowissenschaftlichen Untersuchungsergebnisse.
       ��������                                                                                                      itself inter alia as an uplift of the         borehole and the many years of           land n                                      Entsorgungsnachweis für abgebrannte Brennele-
       ��������������                                                                                                                                                                                                                                   mente, verglaste hochaktive Abfälle sowie langle-
       �����������������                                                                                             crust. Based on data and informa-             ne ote c ton ic obser vat ion pro -                                                  bige mittelaktive Abfälle“; Nagra Technical Report
                                                     �������                                                         tion from a range of sources (geo-            grammes. The lateral extent and                                                      NTB 02-03. Nagra, Wettingen.
       �����������������                                                                                                                                                                                                                             12
                                                                                                                                                                                                                                                        HSK (1999): “Entsorgungsnachweis für HAA/LMA.
       ���������                                                                                                     morphology, subsidence and uplift             thickness of the host rock, and the                                                  Option Endlager im Opalinuston: Beurteilungskon-
                                                                                                                     history, geodesy, Fig. 12), the long-         absence of large fault zones in the                                                  zept für den Standortnachweis. Aktennotiz 23/57“;
                                                                                                                                                                                                                                                        Swiss Federal Nuclear Safety Inspectorate (HSK). HSK,
                                                                                                                     term uplift rate in the Zürcher               central part of the area, are well                                                   Villigen.
                                                                                                                                                                                                                                                     13
                                                                                                                                                                                                                                                        Müller W.H., Naef H. and Graf H.R (2002): “Geologi-
                                                                                                                     Weinland is estimated to be a maxi-           documented. Knowledge of the                                                         sche Entwicklung der Nordschweiz, Neotektonik
                                                                                                                     mum of 100 metres per million                 properties of the host rock, in terms                                                und Langzeitszenarien Zürcher Weinland“; Nagra
                                                                                                                                                                                                                                                        Technical Report NTB 99-08. Nagra, Wettingen.
                                                                                                                     years.                                        of solute transport and engineering
                                                                                                                     In evaluating the long-term evolu-            suitability, is broadly supported, due
                                                                                                                     tion of the region, it is pessimistically     to additional investigations in other
                                                                                                                     assumed that this movement will               exploratory boreholes drilled in
                                                                                               �����
                                                                                                                     continue. It is also assumed that             Northern Switzerland, as well as
                                                                                                                     linear erosion, including the lower-          studies in the Mont Terri Rock
                                                                                                                     ing of the Rhine, will be a maximum           Laboratory. Comparisons with other
                                                                                                                     of around 200 metres over the period          argillaceous formations have shown
                                                                                                                     of the next million years. This means         that the parameter values derived are
Figure 12                                                                                                            that the remaining rock overburden            in the expected range. Knowledge
Annual changes in elevation in Switzerland in relation to a reference point in Aarburg (data based on repeat
                                                                                                                     of, for example, a repository located         of the possible long-term evolution
measurements, Swiss national levelling network[Lit. 13]). Uplifts of more than 1 mm/year can be observed in the
region of the Alps. Uplift can also be measured in most of the central plateau (midlands). In contrast, the north-   at a depth of 650 metres would still          of the tectonic, hydrogeological and
west part of Switzerland shows a tendency towards subsidence.                                                        be 450 metres. Observations have              geochemical conditions also pro-


nagra Bulletin 35

22                                                                                                                                                                                                                                                                                                               23
                                                                                                                                                      Portal zone
                                                                                                                                                      1 Administration building
                                                                                                                                                      2 Operations centre
                                                                                                                                                      3 Ventilation building
                                                                                                                                                      4 Equipment transition area
                                                                                                                                                      5 Conditioning and packaging
                                                                                                                                                         plant for SF/HLW
                                                                                                                                                      6 Rail access
                                                                                                                                                      7 Road access                                                                        Summary
                                                                                                                                                      8 Access tunnel, ramp (sub-surface)
                                                                                                                                                                                                                                           A deep geological repository for
                                                                                                                                                                                                                                           spent fuel (SF), high-level waste
                                                                                                                                                                                                                                           (HLW) and long-lived intermedi-
                                                                                                                                                                                                                                           ate-level waste (ILW) can be
                                                                                                        Shaft head area
                                                                                                                                                                                                                                           constructed using presently avail-
                                                                                                        1 Shaft head frame with air vents                                                                                                  able technology. The expecta-
                                                                                                        2 Construction site office, personnel areas,
                                                                                                                                                                                                                                           tions of society in terms of
                                                                                                           workshop, transformer, etc.
                                                                                                        3 Excavated material dump                                                                                                          monitoring and control can also
                                                                                                        4 Equipment/materials store                                                                                                        be fulfilled. The facility compo-
                                                                                                                                                                                                                                           nents are brought together as a
                                                                                                                                                                                                                                           modular system to form a refer-
                                                                                                                                                                                                                                           ence project and can be modified
                                                                                                                                                                                                                                           later to meet actual conditions
                                                                                                                                                                                                                                           at the site. Information specifi-
                                                                                                                                                                                                                                           cally required for analysing and
                                                                                                                                                                                                                                           demonstrating long-term safety
                                                                                                                                                                                                                                           has been provided.



                    Demonstration of disposal feasibility for high-level waste



                    Concept for facilities and operation
                    of a deep geological repository
                    Introduction                               crystalline basement and in clay was    together with the geological syn-                   and facility components for which     land consists of surface and under-
                    Management of spent fuel (SF),             considered. The strategy developed      thesis report for the Zürcher Wein-                 the feasibility study was conducted   ground facilities (see title picture on
                    vitrified high-level waste (HLW)            by Nagra over the years agrees well     land [Lit. 5] and the report on long-               are brought together as a modular     this double page).
                    and long-lived intermediate-level          with the concept of “monitored          term safety [Lit. 6] .                              system to form a stand-alone refer-   The surface facilities are located in
                    waste (ILW) is based on the concept        long-term geological disposal” as       The facilities and operation concept                ence project. They can be adapted     the portal zone and in the area             Deep geological repository
                    of deep geological disposal, namely        formulated recently by the author-      looks at the feasibility of construct-              later to meet local features and      around the head of the shaft. The           The Swiss Nuclear Energy Law [Lit. 3] calls for disposal
                    long-term, effective isolation of the      ities [Lit. 2, 3] .                     ing a repository in the Opalinus Clay               requirements.                         title picture shows this in the form        of radioactive waste in a deep geological repository.
                    waste in suitable deep rock form-          This article provides an overview of    of the Zürcher Weinland. It also                                                          of a model. The buildings would             The facility must remain accessible over an extended
                                                                                                                                                                                                                                             period of time and monitoring must be possible.
                    ations. The first project studies          the concept for facilities and opera-   provides project-specific input for                  Outline of the geological             resemble a small industrial facility
                                                                                                                                                                                                                                             Long-term protection of man and the environment
                    carried out by Nagra in this respect       tion of a deep geological repository    analysing and demonstrating the                     repository                            and can be integrated well into the         following closure of the facility must be ensured by
                    already lie more than 20 years in          for SF/HLW/ILW[Lit. 4], as prepared     long-term safety of such a repository.             The geological repository in the       landscape.                                  a system of passive safety barriers.
                    the past [Lit. 1] , when disposal in the   for the Entsorgungsnachweis project,    The individual structural elements                 Opalinus Clay of Northern Switzer-


nagra Bulletin 35

24                                                                                                                                                                                                                                                                                                      25
                            Portal zone                           Underground facilities                                                     dient of 12.5 percent and the emplace-
                            The facilities in the portal zone of The underground facilities are con-                                         ment tunnels of around 6 percent,                    �����������������������                                      �����������������������������
                            the access tunnel comprise an nected to the surface by a ramp and                                                corresponding to the regional dip of
                            administration, operations and        a shaft and consist of (see Fig. 1):                                       the Opalinus Clay layer.
                            ventilation building and the infra- • the main facility for spent fuel                                                                                                      ���                                                           ���
                            structure for road and rail access.      and vitrified high-level waste and                                       Waste volumes
                            Integration of a conditioning and        the facility for long-lived interme-                                    For the purpose of designing the
                                                                                                                                                                                                                                                        �������������
                            packaging plant for spent fuel and       diate-level waste                                                       facility, it was assumed that spent            �������������                                               �������������
                            vitrified high-level waste would be • the pilot facility for long-term                                            fuel and radioactive waste (Fig. 2)       ������������������
                            possible. The ma ximum space             control and monitoring of the                                           will arise from a 192 GWe a power




                                                                                                                                                                                                                                                                                                                    �����
                            required would thus be around 300        facility, also following closure of                                     production scenario for the existing                                                                    ����������������
                            by 150 metres.                           the main facility                                                       nuclear power plants. This corre-                                                                           ���������
                                                                 • the test facility (rock laboratory)                                       sponds to an average operating life-
                            Shaft head area                          for performing scientific investi-                                       time for the five power plants of 60




                                                                                                                                                                                                                              ������������
                            Located at the top of the shaft are      gations.                                                                years. For spent fuel, it was assumed                                                                                                                   ������
                            the shaft head frame and various The overall dimensions of the dis-                                              that about 30 percent of the fuel
                                                                                                                                                                                           �������������
                            auxiliary buildings. The space        posal zone are approximately 2650                                          elements would go for reprocessing
                            requirement is approximately 100 by metres in length and around 700                                              and the remainder would be dis-
                            100 metres.                           metres wide. The repository will be                                        posed of directly in a deep repository.                                                                     ���������������������������
                                                                  constructed at a depth of 600 to 900                                       The resulting volumes can be seen                                                                           ��������������������
                                                                  metres. The access tunnel has a gra-                                       in Figure 3.                                                                                                �������                                        �����������������
                                                                                                                                                                                                                                                         ��������                                                                  ���������������




                                                                                                                                                                                                                                                                                     �������




                                                                                                                                                                                                                                                                                                                                 ������
                                                                                                                                                                                                                                                                            ������




                                                                                                                                                                                                                                                                                                                        ������
                                                                                                                                                                                                                                                            ������                                                                                   Figure 2
                                                                                                                                                                                                                                                                                                                    ������������������
                                                                                            ����������������������                                                                                                                                             �������                                                                               Containers for disposal
                                                                                                                                                                                                                        ���                                                                                   �����������                            of spent fuel (left),
                                                                                                                                                                                                                     ���
                                                                                                                                                                                                                                                         ����������

                                                                                                                                                                                                                                                                                                                                                     high-level waste (top




                                                                                                                                                                                                                                                                                     �������
                                                                                                       ��                                                                                                                                                                                                                                            right) and long-lived




                                                                                                                                                                                                                                                                                                                                 ������
                                                                   ��������������                        ���




                                                                                                                                                                                                                                                                                                                        ������
                                                                                                                                                                                                                                                                            ������
                                                                                                               ����                                                                                                                                                                                                                                  intermediate-level
                                                                   �����������                                     ���
                                                                                                                        �����                                                                                                                                                                                                                        waste (bottom right).
                                                                                                                 ���
                                                                                                                      ���
                                                                                                                             ��                                                                                                                            ������
                                                                                                                                �                                                                                                                              �������




                                                               ���������������                   �������������           ��������������                                                                                                      �������������
                                                                      ������                                                                                       ������������
                                                                                             �����������������                  �����
                                                                                                                                                                                                    ����������                ��������������������                                               ���������������������
                                                                                                                                                                         �����������
                                                                                                                                                     ��
                                                                                                                                                  ��� �




                                                                                                                                                                                                                              �����                                                              ������������������������
                                                                                                                                               ��� ���




                                                                                                                                                                         ������
                                                                                                  ��




                                                                                                                                             �� ���
                                                          ��




                                                                                                 ���
                                                      ��




                                                                                                                                                                                                    �
                                                                                                                                          ��� ���
                                                                                               ��




                                                                                                                                                                ������������
                                                    ���
                                            ���
                                ���������




                                                                                                                                             �
                                                      �




                                                                                                                                                                �����������
                                            ��

                                                  ���




                                                                                             ���������������                                                                                                                                                                                                                                         Figure 3
                                                                                    �� ��
                                             ����




                                                                                      ��




                                                                                                                                                          ������������
                                                                                  �� �
                                                                               ��� ��




                                                                                                                                                                                                                                                                                                                                                     The waste volumes
                                               �
                                            ��




                                                                             �� ���




                                                                                                                          �������������                                                                                                                                                                                                              for a 192 GWea
                                                                          ��� �
                                                                      ���� ��




                                                                                                                       �����������������                                                                                                                                                                                                             electricity production
                 Figure 1                                                                                                                                                                                                                                                                                                                            scenario assumed for
                                                                    �������������������                �����
       Overview of the                                                                                                                                                                                                                                                                                                                               the Opalinus Clay
           underground                       ������������������                               ��������������������                                                                                                                                                                                                                            �      Project [cf. Lit. 4] . The
                                                                                                                                                                                                    ��������������                             �������������                                                          ��������������
     facilities of a deep                    �����������������                                                                                                                                                                                                                                                                                       containers are shown
                                             ������������������������������                                                                                                                                                                                                                    ������������������������������
               geological                                                                                                                                                                                                                                                                      ����������������������������������������              in the same relative
      repository for SF/                                                                                    ������
                                                                                                                                                                                                                                                                                                                                                     size scale.
               HLW/ILW.



nagra Bulletin 35

26                                                                                                                                                                                                                                                                                                                                                                            27
                        Safety concept for the                   Achieving these targets is ensured         installations, as well as handling         Waste emplacement                        hydraulic wagon and the canister is
                        operating phase                          by:                                        devices and transport methods, are         Preparation for emplacement              then transferred to the emplacement
                        The aim of all the safety-oriented      • Defining the requirements to be            based on proven state-of-the-art           Spent fuel (SF) and vitrified high-       trolley (Fig. 4a, 4b).
                        technical, administrative-opera-            met by the waste to be emplaced         technology. Handling of radioactive        level waste (HLW) are welded into        Once this has been done, the canis-
                        tional and monitoring measures in           (solidification, packaging)              waste is part of routine operation in      thick-walled steel canisters in prepa-   ter is moved on the trolley to its
                        a geological repository is to prevent   • Technical measures (layout of the         every nuclear facility, as is its trans-   ration for emplacement (Fig. 2).         emplacement location. Because the
                        operational perturbations, incidents        facility and design of technical        port.                                      The HLW emplacement canisters            tunnel is inclined, this process can
                        and accidents and to avoid unaccept-        installations and equipment)            The entire facility is run and moni-       are two metres long and weigh            be achieved by gravity alone, with
                        able radiation exposure to operating    • Operational-administrative meas-          tored from a command centre in the         around eight tonnes; the SF canis-       the trolley being secured using a
                        personnel, visitors and the popula-         ures (defining work procedures           surface reception facility. In terms       ters are a maximum of five metres         cable attached to the winch locomo-
                        tion living in the vicinity of the          and personnel conduct)                  of radiation protection, the reposi-       long and weigh thirty tonnes.            tive. Once the emplacement position
                        facility. For normal operation, the     • Monitoring measures (entry con-           tory is divided into a controlled and      The long-lived intermediate-level        has been reached, the bentonite sup-
                        ALARA (as low as reasonably achiev-         trol, radiation monitoring at           a non-controlled zone and access           waste (ILW) is packaged into con-        port blocks and the canister are
                        able) principle also has to be taken        critical locations, personal dosim-     rules are applied in accordance with       crete containers in the surface recep-   deposited together and the trolley is
                        into account for radiation exposure.        etry, critical operating parame-        the guidelines of the Swiss Federal        tion facility (Fig. 2) and the remain-   pulled out of the tunnel using the
                                                                    ters).                                  Nuclear Safety Inspectorate (HSK)          ing voids in the containers are          winch.
                                                                 The waste is delivered in a form suit-     and the provisions of the Radiation        backfilled with mortar. The external      The backfill wagon – secured by the
      ����
                                                                 able for emplacement (SF and HLW           Protection Ordinance. Used air and         container dimensions are a maxi-         winch – then drives into the tunnel.
 ����������                                                      in massive safety containers) and is       effluents undergo continuous moni-          mum of 2.45 metres and they are up       The bentonite clay, which has been
                                                                 packed on site into emplacement            toring and items from the controlled       to forty tonnes in weight.               compressed into pellets, is intro-
                                                                 canisters. Technical equipment and         zone require clearance.                                                             duced as a backfill using spiral
                                                                                                                                                       Spent fuel and high-level waste          conveyors before the next canister is
                                                                                                                                                       Emplacement of spent fuel and high-      emplaced. Once a tunnel is full, it is
                                                                                                                                                       level waste basically follows the same   sealed in the transition area
                                                                                                                                                       procedure, but the HLW canisters
                                                                                   ������������������
                                                   ������                                                                                              are significantly shorter and lighter.    Long-lived intermediate-level
                                                   ����������                               �������������������
                                                                                            �������������������������                                  The following description relates to     waste
                             �����������
                    ���������������������
                                                                                                                                                       the spent fuel canisters.                Once the mortar backfill in the
                                                                                                                                                       In the operations building of the        containers has been allowed to
                        Figure 4a                                                                                                                      surface reception facilit y, the         harden in the surface reception facil-
                                                                                                                        ����������������
                        SF canister in the central area: the                                                                                           emplacement canisters with the           ity, the concrete containers are
                        tunnel locomotive has taken over                                                                                               spent fuel elements are transferred      loaded onto the rack railway and
                        the canister (in transport shielding)
                        from the rack locomotives.                                                                                                     into the internally used transport       transported to the central area
                                                                                                                                                       shielding; after being checked and       underground; here the tunnel loco-
                                                                      ���������                                                                        registered, they are transported to      motive takes over for further trans-
                                                                     ���������
                                                                                                                                                       the underground central area using       port to the unloading station of the
                                                                        �������������������                                                            the rack railway; in the central area,   emplacement tunnel. Once there,
                                                                                                                                                       transport is taken over by the tunnel    the containers are deposited on the
                                                                                                                                                       locomotive (Fig. 4a).                    tunnel floor and stacked (Fig. 5).
                                                                                  ���������������                                                      This locomotive brings the load to       Depending on container type, a
                                                                                                                                                       the transition area of an emplace-       stack consists of two or three con-
                                                                SF canister in the transition area: the canister has already been removed from the     ment tunnel, with the hydraulic          tainers.                                 Figure 4b
                                                                transport shielding and transferred from the transload equipment to the                wagon being linked into the compo-       Once a stack is complete, the air-       Film sequence: transfer of an SF canister in the transition
                                                                emplacement trolley.                                                                                                                                                     area at the beginning of an emplacement tunnel;
                                                                                                                                                       sition on the way. In the transition     cushion transporter moves beneath        emplacement in the tunnel and backfilling. Transport
                                                                                                                                                       area, the fuel element canister is       the stack, raises it by a few centime-   and emplacement of a HLW canister basically follow the
                                                                                                                                                       pushed onto the transload equip-         tres and moves it to its emplacement     same procedure.
                                                                                                                                                       ment using the cylinder of the           position. Once the tunnel is com-


nagra Bulletin 35

28                                                                                                                                                                                                                                                                                                     29
                                                                                                                                                           sure of the entire repository. Filled     pilot facility can be monitored from
                                                                                                                                                           ILW tunnels are then sealed at the        the SF/HLW observation tunnel
                     ���������������������������������������������������������������                                                                       same time as the first tunnels in the      and one ILW emplacement tunnel                               �����������������
                                                                                                                                                           main facility are being constructed.      from the ILW observation tunnel                            ���������������������
                    �������������                                                    ��������������������                                                  This work is done via the construc-       (phase of monitoring the pilot facil-
                                                                                                                                                           tion and ventilation shaft. For safety    ity, Fig. 8).
                                                                                                                                                           reasons, no SF/HLW tunnels are                                                                            ��������������������
                                                                ��������������������              �������������������
                                                                                                                                                           constructed in advance by way of          Closure of the entire facility                                      �����������
                                                                                                                               �����������                 reserve. This means that tunnels are      After an extended monitoring phase,
                                                                                                                               ������
                                                                                                                                                           constructed as required during            the decision is made to close the
                                                �������




                                                                                                                                                           emplacement to keep pace with the         entire facility and all accesses that




                                                                                                                                                  ������
                                                                                                                                                           emplacement operation. The time           remain open are backfilled.                                    �����������������������
                                                                   �����������                                                                             required for filling the pilot facility    The time required for closing the
                                                                   �����������                                                                             and the ILW disposal zone is esti-        installations located in the Opalinus
                                                                                                                                                           mated at two years; for the SF/HLW        Clay is estimated to be around one
                                                                                                                                                           tunnels, the time is around 15 years,     year; for the rest of the access tunnel
                                                                                                                                                           including some reserve. This means        the time is expected to be around                           ������������������������������
                       ������                                                           ������
                                                                                                                                                           that, for 27 tunnels, around two          three to four years.
                                                                                                                                                           SF/HLW tunnels will have to be            The concept for realising the reposi-
                          Figure 5                                                                                                                         constructed per year.                     tory foresees stepwise backfilling and
                          The containers delivered by the tunnel locomotive are unloaded in the unloading station and then brought with an air-                                                      sealing leading to complete closure                         ���������������������������
                          cushion transporter to their emplacement position in the tunnel.                                                                                                                                                                         �����������������������
                                                                                                                                                           Monitoring phase                          of the entire facility. The concept is
                                                                                                                                                           At the end of emplacement opera-          based on the objective of achieving
                                                                                                                                                           tions, all emplacement tunnels are        optimum protection of the waste
                                                                                                                                                           sealed (Fig. 7) and a first monitor-       from internal and external influences
                                                                                                                                                           ing phase begins. The duration of         and from the actions of third parties.                            ����������������
                          pletely full, the installations are        access tunnel and the installations         Delivery of the waste                     this phase has not yet been decided,      In every situation, a degree of revers-
                          removed and remaining voids are            of the rock laboratory is estimated         It is planned to transport the waste      but it should not continue for too        ibility that is appropriate to the
                          backfilled with mortar.                     at around six years.                        to the repository site by rail. The       long.                                     phase in question should be main-
                                                                                                                 transport frequency is expected to                                                  tained.
                                                                                                                                                                                                                                                                     ������������������������
                          Construction and closure                   Repository construction                     be around one delivery per month,         Closure of the main facility              Closure of the repository involves a
                          of the repository                          During construction, all facility           with two to three containers for high-    The first monitoring phase ends           system of staged passive safety bar-
                          Construction and closure of a geo-         components and technical infra-             level waste or spent fuel. These are      with the closure of the main facility     riers consisting of tunnel backfill,
                          logical repository proceed in a step-      structure required for emplacement          packed into emplacement canisters         (Fig. 8). The construction and            concrete plugs and seals, which
                          wise manner (see Fig. 6):                  of radioactive waste are built and          in the surface facilities. The interme-   operations tunnel, the ventilation        make further safety and monitoring                            ����������������������������
                                                                     installed. After around half a year         diate-level waste will also arrive by     tunnel and the construction shaft         measures unnecessary.
                          Underground exploration                    for additional development and              rail.                                     are all backfilled and special seals
                          Once the surface investigations are        installation by the various contrac-                                                  are installed (see e.g. Fig. 9). The      Retrievability
                          complete, an access tunnel is con-         tors, the time required for this            Emplacement operations and                time required to close the main           The waste can be retrieved at any
                                                                                                                                                                                                                                                                    ��������������������������
                          structed together with a test facility     second phase – actual repository            extension of the facility                 facility is estimated to be around        time. To do this, the seals and the
                          (rock laboratory) at the planned           construction – is estimated to be           Once the construction work is suf-        three years.                              backfill material would have to be
                          disposal level. In this test facility,     around four years. It is planned to         ficiently far advanced, disposal of                                                  removed. Once the entire facility has
                          additional information on the site         work simultaneously at several loca-        ILW in the emplacement tunnels            Monitoring of the pilot facility          been closed, the effort involved in
                          can be obtained and parameters that        tions, allowing this work-intensive         and of SF/HLW in the pilot facility       Once the main facility has been           retrieving the waste is correspond-       Figure 6
                          are important for the long-term            phase to be completed in a relatively       can begin. This allows a long obser-      closed, access to the central area, the   ingly greater.                            Many steps lie between the first investigations from the earth‘s
                                                                                                                                                                                                                                               surface and the final closure of a deep repository.
                          safety analysis can be verified. The        short time.                                 vation period to be achieved for the      test facility and the observation
                          time required for constructing the                                                     pilot facility, up to the time of clo-    tunnels still remains possible. The


nagra Bulletin 35

30                                                                                                                                                                                                                                                                                                               31
                                                                                                                                                                                                                                    Literature references
                                                                                                                                                                                                                                    1
                                                                                                                                                                                                                                        Nagra (1980): “Projektstudie für die Endlagerung von
                              ����������������                                                                                                      �������������                                                                       hochaktiven Abfällen in tiefliegenden geologischen
                                                                                                                                                                                                                                        Formationen sowie für die Zwischenlagerung“;
                                                    ��������������                                                                                                                                                                      Nagra Technical Report NTB 80-02. Nagra, Wettin-
                                                    �����������             ��                                                                                                                      ��������
                                                                                                                                                                                                                                        gen.
                                      �����������                             ���                                                                                                                                                   2
                                                                                                                                                                                                                                        EKRA (2000): “Disposal Concepts for Radioactive
                                      ������                                     ����                                                                                              �����
                                                                                      ��                                                                                                                                                Waste“; Expert Group on Disposal Concepts for
                                                                                           ����                                                                                    ���              ������������������
                                      ����                                                     ���                                                                                                                                      Radioactive Waste (EKRA).
                                                                                     ���
                                                                                                  ��                                                                                                                                3
                                                                                                                                                                                                                                        NEA/OECD (2003): “Switzerland – Act on Nuclear
                                      ����                                              ���                                                                                                                                             Energy (21 March 2003)“; Nuclear Law Bulletin,
                                      ����                                                                                                          ���������������                                 ������������������                  Supplement to No. 72. Nuclear Energy Agency
                                                                                                                                                                                                                                        (NEA), Organisation for Economic Co-operation and
                                                                                                                                                                                                    ���������������������������         Development (OECD).
                                                                                                                ����������                                                                                                              Nagra (2002): “Projekt Opalinuston: Konzept für
                                                                     �������������                              ����������                                                                          ���������������������������     4

                                                                                    ��������������                               ������������                                                                                           die Anlage und den Betrieb eines geologischen
                 Figure 7       ������������������                                                                                                                                                  ����������������������              Tiefenlagers. Entsorgungsnachweis für abgebrannte
                                �������                          ������������������������
    Situation following                                                                                                                                                                                                                 Brennelemente, verglaste hochaktive sowie langle-
                                                                                                                                                                                                                                        bige mittelaktive Abfälle“; Nagra Technical Report
         completion of                                                                                                                                                                                                                  NTB 02-02. Nagra, Wettingen.
                                              �
                                           ��




          emplacement                                                                                                                                                                                                               5
                                                                                                                                                                                                                                        Nagra (2002): “Projekt Opalinuston: Synthese der
                                         ��




                                                                                                                              �����������                                                                                               geowissenschaftlichen Untersuchungsergebnisse.




                                                                                                                                                                      ��������
 operations and during
                                      ���




                                                                                                                              ����������                                                            �������������������                 Entsorgungsnachweis für abgebrannte Brenn-
                                  ���




   the first monitoring                                                                                                   ����������������������     �������������                                   �������������������                 elemente, verglaste hochaktive sowie langlebige
                                ����




 phase. All the tunnels                                                                                                                                                                                                                 mittelaktive Abfälle“; Nagra Technical Report NTB
                                  �
                               ��




                                                                                                                                                                                   �����
    that are filled with                                                                                              ������������
                                                                                                                                                                                                                                        02-03. Nagra, Wettingen.
                                                                                               �������������                                                                                                                        6
                                                                                                                                                                                                                                        Nagra (2002): “Project Opalinus Clay: Safety report.
   waste are backfilled
                                                                                            �����������������       ������������������                                                                                                  Demonstration of disposal of spent fuel, vitrified
  and closed with seals                                                                                                                                                                                                                 high-level waste and long-lived intermediate-level
                                                                                                                    ������                                                                          ������������������������
   and concrete plugs.                                                                                                                                                                              ������������������������            waste (Entsorgungsnachweis)“; Nagra Technical
  The other tunnels, as                                                                                                                                                                             ������������������                  Report NTB 02-05. Nagra, Wettingen.
  well as the shaft, are                                           ��������������������                                  �����
                                                                                                                                                                                                    ������������������
          still open and       ������������������
                               �����������������        �������������������                                                                                                                         ������������������
     accessible without        ������������������������������
radiological protection                                                                                                                                                                             ����
               measures.
                                                                                                                                                                       ������������������
                                                                                                                                                                ��������������������
                              ����������������������������                                                                                               �����������������������

                                                    ��������������
                                                    �����������             ��
                                      �����������                             ���
                                      ������                                     ����
                                                                                      ��
                                                                                           ����
                                      ����                                                     ���                                                Figure 9
                                                                                                  ��
                                      ����                                           ���
                                                                                           ���
                                                                                                                                                  Proposed concept for shaft sealing.
                                      ����                                                                                                                                                                                          DVD “Deep geological repository in
                                                                                                                                                                                                                                    Opalinus Clay, concept for repository
                                                                                                                ����������                                                                                                          facilities and operations”. Nagra has
                                                                     �������������                              ����������       ������������
                                                                                    ��������������
                                ������������������
                                                                 ������������������������
                                                                                                                                                  Conclusion                                                                        produced a DVD on the topic covered
                                                                                                                                                                                                                                    by this article. The DVD is available
                                �������
                                                                                                                                                  Based on the work carried out, the        retrievability of emplaced waste is     from Nagra free of charge in German/
                                                                                                                                                  following conclusion can be drawn:        also assured. Spatial reserves exist    English
                                             �
                                         ��
                                       ��




                                                                                                                              �����������         A deep geological repository for          and the concept for facilities and
                                     ���




                                                                                                                              ����������
                                  ���




                                                                                                                         ����������������������   SF/HLW/ILW can, with existing             operation offers a high degree of
                  Figure 8
                                ����




                                                                                                                                                  technology and in accordance with         flexibility for developing the project
                                  �




 Situation after closure
                               ��




     of the main facility                                                                      �������������         ������������                 legally prescribed safety standards,      in the future n
  and during the phase                                                                      �����������������       ������������������            be constructed, operated, monitored
of monitoring the pilot                                                                                             ������
      facility. The closed
                                                                                                                                                  and closed within a few years in the
            section of the                                                                                                                        Opalinus Clay of the Zürcher Wein-
                                                                                                                         �����
  repository is secured                                            ��������������������
                               ������������������                                                                                                 land. Societal pressure to have
    by sealing systems.        �����������������        �������������������
                               ������������������������������                                                                                     monitoring and control has been
        The parts of the
facility shown in green                                                                                                                           met, as formulated in the new
      are still accessible.                                                                                                                       Nuclear Energy Law [Lit. 3] . The


nagra Bulletin 35

32                                                                                                                                                                                                                                                                                             33
                                                                                                                                                                                                                               Summary

                                                                                                                                                                                                                               The safety case – the synthesis
                                                                                                                                                                                                                               of all arguments and analyses
                                                                                                                                                                                                                               related to long-term safety,
                                                                                                                                                                                                                               including the results of a quan-
                                                                                                                                                                                                                               titative evaluation of system
                                                                                                                                                                                                                               performance – is the final step
                                                                                                                                                                                                                               in the “Entsorgungsnachweis“.
                                                                                                                                                                                                                               This article presents an overview
                                                                                                                                                                                                                               of this synthesis. It is concluded
                                                                                                                                                                                                                               that permanent disposal of spent
                                                                                                                                                                                                                               fuel (SF), vitrified high-level
                                                                                                                                                                                                                               waste (HLW) and long-lived
                                                                                                                                                                                                                               intermediate-level waste (ILW)
                                                                                                                                                                                                                               is feasible from the point of view
                                                                                                                                                                                                                               of safety in the proposed repos-
                                                                                                                                                                                                                               itory in the potential siting area
                                                                                                                                                                                                                               in the Zürcher Weinland.




                    Demonstration of disposal feasibility for high-level waste


Analysis and demonstra-
tion of long-term safety
                    The safety case                         a demonstration that the protection       questions is discussed in the context       the diverse safety functions of the System with multiple                      waste and fissile materials (in
                    If the geological investigations and    objectives laid down by the safety of future stages of repository plan-               proposed disposal system.           safety barriers                           spent fuel) in the deep repository.
                    the engineering project represent       authorities in Guideline R-21[Lit. 1] are ning and development.                   •   Assessing the robustness of the Emplacement                                   Once the access routes have been
                    important steps on the way to dem-      observed. The safety case is docu- The safet y ana lysis in Project                   disposal system with respect to Figure 1 shows schematically how the          backfilled and sealed, the likeli-
                    onstrating permanent safe waste         mented in a safety report[Lit. 2], which Entsorgungsnachweis has the follow-          uncertainties and the effects of long-term safety of the system is            hood of undesirable human intru-
                    disposal, then making the case for      describes the system and its evolu- ing specific objectives:                           phenomena that could perturb        achieved: with a system of “made-to-      sion and prohibited use of the
                    long-term safety can be seen as the     tion, defines its safety functions and • Evaluating the suitability of the             the sa fet y functions of the       measure” multiple safety barriers that    fissile material is very small. The
                    final and decisive step.                 shows the effectiveness of the various       Opalinus Clay in the Zürcher             system.                             fulfils a range of safety functions:       likelihood of inadvertent human
                    The safety case is based on argu-       barriers and of the system as a whole.      Weinland as a potential host rock     •   Providing a basis for discussion • Isolation from the human envi-             intrusion (e.g. by drilling) is re-
                    ments and analyses of the long-term     Arguments and analyses related to            for a deep repository from the           on future planning of waste man-       ronment: The safety of man and         duced by selecting a disposal
                    safety of the proposed disposal         safety are described and the signifi-         viewpoint of long-term safety.           agement strategies.                    the environment is ensured by          region where, from a present-day
                    system. This includes, in particular,   cance of uncertainties and open • Improving the understanding of                                                             containment of the radioactive         viewpoint, there are no economi-


nagra Bulletin 35

34                                                                                                                                                                                                                                                                    35
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                                                                              ������������

                                                                         ���������������������������������                          Figure 2
                                                                         ������������                                               The activity of spent fuel and high-level waste decreases in the first 100 years following emplacement (i. e. 140 years
                                                                         � ���������������������������������������                  following removal from the reactor) to around 1/10 (top) and, after around 400 years, to less than 1/100 of the initial
                                                                         ������������������������                                   activity (cannot be shown on graph). The bottom graph shows the decrease with time in the activity contained within a
                                                                         � �����������������������������                            spent fuel and a high-level waste canister; this is shown on a logarithmic scale to make the decrease with time more
                                                                                                                                    clearly visible.

                                                                          ��������������
                                                                          ������������
                                                                          � ������������������������������������������                                                                                                                                     ����������������������������������
                                                                               ���������������������������������������                                                                                                                                     ������������������������������
                                                                          � � ������������
                                                                          ������������������������
                                                                          � �������������������������������������������             cally viable resources present (no                                 while the waste is still completely                                           ���
                                                                               ��������������������������������������               conflict of use). Finally, careful                                  isolated by the intact canisters.
                                                                          � ������������������������������������������                                                                                                                                                                                                                                                                    Figure 3
                                                                                                                                    site selection ensures that there                                  The steel canisters for spent fuel                                            ��                                                                                                   Loss of radiotoxicity




                                                                                                                                                                                                                                                                                                                                                        �������������������������������
                                                                                                                                                                                                                                                        ��������������������������
                                                                                                                                    will be no geological events or                                    and high-level waste ensure com-                                                                                                                                                   of emplaced spent




                                                                                                                                                                                                                                                                                                                         ����������������������������
                                                                          ������������������                                        unfavourable processes that                                        plete containment for a period of                                                                                                                                                  fuel (SF) due to
                                                                                                                                                                                                                                                                                     ��
                                                                          ������������                                              would compromise the long-term                                     at least 10,000 years. Even after                                                                                                                                                  decay in the
                                                                          � �� ����������������������                                                                                                                                                                                                                                                                                     Reference Case in
                                                                          � �� ��������������������������������������������         stability of the system.                                           the canisters fail, a series of geo-                                                                                                                                               different compo-
                                                                                                                                                                                                                                                                                     ��
                                                                               ������������                                     •   Long-term containment and                                          chemical immobilisation and re-                                                                                                                                                    nents of the system
                                                                          ������������������������
                                                                                                                                    radioactive decay within the                                       tardation processes ensure that                                                                                                                                                    (see text-box on




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                                                                          � �� ��������������������������������������
                                                                                                                                                                                                                                                                                     ��                                                                                                   page 39). Only very
                                                                                                                                    disposal system: The activity of                                   the radionuclides remain largely




                                                                                                                                                                                                                                                                                                          ��������
                                                                               ���������������������������������                                                                                                                                                                                                                                                                          small proportions
                             ���������                                    � �� �����������������������������������������            the emplaced spent fuel and ra-                                    contained within the engineered                                                                                                                                                    reach the geosphere
                                                                                                                                                                                                                                                                                      �
               Figure 1                                                                                                             dioactive waste decreases with                                     barriers of the repository and in                                                                                                                                                  (Opalinus Clay host
The system of multiple     ���������������                                                                                                                                                                                                                   ����������������                                                                                                             rock / neighbouring
                                                                                                                                    time (cf. Fig. 2). A large compo-                                  the immediately surrounding
     safety barriers for                                                                                                                                                                                                                                     ������������������������������������������                                                                                   rock) and the
spent fuel and vitrified                                                                                                             nent of the radioactivity that was                                 rock, where a large majority of                       ���������������������������
                                                                                                                                                                                                                                                                                                                                                                                          biosphere.
      high-level waste.                                                                                                             originally present will decay away                                 them will decay (Fig. 3).


nagra Bulletin 35

36                                                                                                                                                                                                                                                                                                                                                                                                                37
                                                                     •   Attenuation of releases to the          stability of the engineered barriers
                                                                         environment: Although com-              and is itself stable due to a range        ���������������������������������������������������������������������������
                 ���������������������                                   plete confinement cannot be             of chemical buffering reactions.
                    ���������������                                      provided over all relevant times Particularly for SF and HLW, the                                                                                                             �����������������������������������������������
                                                                                                                                                              ���������                      ������������������                          ��������������               ��������������������
                                                                         for all radionuclides, release rates following can be added:                         ������                         ������                                      ������            ���������������������������������
                                                                                                                                                              ����                           ������                                      ������
                 ����������������������������������                      of radionuclides from the waste • The waste matrices, which are                      ��������������������           �����������������������                     ������������
                       �������������������                                                                                                                    ����������������������         �����������������������                     ������������                                                ��
                                                                         forms are low, particularly from        stable under the expected condi-
                                                                                                                                                              �����������������������        �������������������                         ������������        ���
                                                                         the stable spent fuel and high-         tions.                                       ��������������                 ���������������������������                 ������������
                                                                                                                                                              ������������������������       ����������������������                      ������������                                       ���
                                                                         level waste forms. Furthermore, a • The emplacement canisters, which                 ���������������                ���������������
           ���������������������������������������������                 number of processes attenuate           are mechanically stable and cor-             �������������������������      �����������������                           ������������                                       ��
              ������������������������������������                                                                                                            ������������������             ��������������������                        ������������
                                                                         releases during transport towards       rosion-resistant and ensure com-                                                                                                                              ���

                                                                         the surface environment, and            plete containment of the waste for           �������������������������      ��������������������������������������      ������������                                         ��
                                                                                                                                                              ���������������������          ��������������������                        �����                          ���
                                                                         limit the concentrations of radio-      a considerable period of time.               ���������                      ���������������������                       ������������                                       ���
                      �������������������������                          nuclides in that environment. • The bentonite buffer as a well-
                                                                                                                                                              ����������������               ��������������������                        �����
                            �����������                                  These include radioactive decay         defined medium between the                                                  ��������������������������������            ������������
                                                                                                                                                                                             ������������������������������              ������������                                                         ��
                                                                         during slow transport through           canisters and the host rock, with                                           �����������������������������������������   ������������                    ���
                                                                         the barrier provided by the host        properties similar to those of the                                          ���������������������������������           ������������                                        ���
                                                                                                                                                                                             ��������������������
                                                                         rock and the spreading of released      rock. The bentonite ensures that                                            �����������������������                     ������������
                    ����������������������������                         radionuclides in time and space         the effects of the emplacement
                                                                                                                                                              �������������������������      ��������������������������������            �����
                                                                         by, for example, diffusion, hydro-      tunnels and the heat-producing                                              �������������������������������             ������������                                                             ��
                                                                                                                                                                                             ����������������������                      �����                                                     ���
                                                                         dynamic dispersion and dilu-            waste on the host rock are kept to
                                                                         tion.                                   a minimum. It also forms an ef-              ���������������������������    ���������������������������                 ������������             ���                       ��
                    �����������������������������                                                                                                             �������������������������      ��������������������                        ������������
                         �������������������                                                                     fective transport barrier for ra-                                                                                                                       ���
                                                                      Pillars of safety                          dionuclides and a favourable en-




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                                                                                                                                                                                                                                                                                      ���������




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                                                                                                                                                                                                                                                                                                                                 �����



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                                                                                                                                                                                                                                                                                                                                                      �



                                                                                                                                                                                                                                                                                                                                                               ���
                                                                                                                                                                                                                                                                                                                                                          ��
                                                                      Certain features and properties of the     vironment for ensuring the long-
                                                                      disposal system play a key role in         term performance of the canisters
                 ����������������������������������                   providing safety. These can be             and the waste matrices.                                                                                                                                                                                ���������������������������
                    ������������������������
                                                                      termed the “pillars of safety”:
                                                                     • The deep underground location A broad spectrum of cases
                                                                                                                                                        Figure 5
                                                                         of the repository, in an environ- In order to evaluate long-term safety,       To evaluate long-term safety, a wide range of assessment cases was considered. Uncertainties were taken into account by considering a range of scenarios
                    ����������������������������
                                                                         ment where human intrusion is        the relative significance of the differ-   or other top-level groupings of cases (6), conceptualisations (total of 29) and parameter sets (total of 58). The horizontal red bars correspond to the
                                                                         very unlikely and where there are    ent properties of the disposal system     spectrum of calculated dose maxima for each waste form and in each scenario or grouping of assessment cases. All doses lie well below the limit of 0.1
                                                                                                                                                        millisieverts per year (mSv/a) set by the safety authorities, in the case of the Reference Scenario by several orders of magnitude.
                                                                         no geological events or processes    and the ongoing processes has to be
                                                                         that would be unfavourable for discussed and the cases that have to
               ����������������������������������                        long-term stability.                 be analysed quantitatively must be        tion of the system are investigated by      relating to the biosphere. The cases
                         ����������������                            • A host rock with a low hydraulic identified (Fig. 4). The cases are              defining alternative scenarios. For          established to test system robustness               The Reference Case
                                                                         conductivity, a fine, homogene- defined in terms of the scenarios that           each scenario, various cases are estab-     are termed “what if?” cases, since                  It is assumed in the Reference
                                                                                                                                                                                                                                                        Case that the dissolution of the
                                                                         ous pore structure and self-sealing they address, the ways in which proc-      lished to explore the effects of more       they involve phenomena and param-
                                                                                                                                                                                                                                                        SF and HLW matrix occurs
                                                                         properties; this presents an effec- esses are conceptualised and the           detailed conceptual and parameter           eter values that are outside the range              slowly, strongly reducing condi-
           �������������������������������������������                                                                                                  uncertainties. The Reference Case,          supported by scientific evidence. The                tions prevail in the near-field
                                                                         tive barrier to radionuclide trans- parameter sets used, as shown sche-
                                                                                                                                                        which is defined in Figure 5, is one         point here is not to analyse realisti-              (with high sorption and low
                                                                         port and a favourable environ- matically in Figure 5.
                                                                                                                                                                                                                                                        solubilities for many radionu-
                                                                         ment for the engineered barrier The starting point for the analyses is         specific case within the Reference           cally conceivable cases but to obtain               clides), that nuclide transport
                                                                         system.                              the Reference Scenario, in which it       Scenario.                                   a more in-depth understanding of                    in the near-field is by diffusion
Figure 4                                                                                                                                                Other groups of cases are established       the robustness of the disposal system.              and that transport in the Opali-
                                                                     • A chemical environment that is assumed that the disposal system
Scheme showing the procedure selected by Nagra for making the                                                                                                                                                                                           nus Clay is also very slow due
safety case for a deep geological repository for spent fuel, high-       provides a range of geochemical      evolves broadly according to expecta-     to investigate system robustness, the       To restrict the number of “what if?”
                                                                                                                                                                                                                                                        to the extremely small water
level waste and long-lived intermediate-level waste.                     immobilisation and retardation       tions. The effects of uncertainties       effects of options for system design        cases, only those that would have a                 flow.
                                                                         processes, favours the long-term     that affect the broad path of evolu-      and the influence of uncertainties           negative effect on the key properties


nagra Bulletin 35

38                                                                                                                                                                                                                                                                                                                                                                   39
                                          of the safety pillars are considered.                already exist today will undergo           latory guideline). The Reference
                                          Even if the list of these cases is not               reprocessing.                              Case (see Figs. 5 and 6) is as much
                                          comprehensive, it serves to illustrate                                                                                                                                     �����������������������������������������������������������
                                                                                               An overview of the results of the          as three orders of magnitude lower.
                                          that the system is still safe, even                  calculations is shown in Figure 5.         The highest values in Figure 5 –
                                          under extreme conditions.                            Figure 6 shows the evolution with          which are still about a factor of ten
                                                                                                                                                                                                                     �� ��
                                                                                               time of the total annual dose for the      below the guideline – result from
                                           Results of the analyses                             Reference Case (sum of the contribu-       scenarios with inadvertent human                                           �� ��

                                          Model calculations of radionuclide                   tions from SF, HLW and ILW). The           intrusion into the sealed repository                                       �� ��                                                                                ������������������������������������




                                                                                                                                                                                         �������������������������
                                          release into the geosphere and, sub-                 range of fluctuation of the calculated      (drilling) and from “what if?” cases                                       �� ��
                                          sequently, into the biosphere were                   dose maxima (Fig. 5) reflects uncer-        with extremely pessimistic parameter                                                                                                                            �����������������������������������
                                          carried out for the individual assess-                                                                                                                                     �� ��                                                                                ����������������������
                                                                                               tainties in the parameter values that      values for the near-field and the geo-
                                                                                                                                                                                                                                                                                              ��
                                          ment cases and the resulting dose                    were used (e. g. geochemical datasets      sphere.                                                                    �� ��
                                          rates were determined. The waste                                                                                                                                                                                                      ���
                                                                                               for sorption and solubilities), in                                                                                    �� ��
                                          volumes considered are based on an                   conceptual assumptions (regarding          Conservative approach                                                      �� �                                             ���
                                          assumed 60-year lifetime for the five                 e. g. preferential release along tunnels   and safety reserves                                                             �
                                          currently operating nuclear power                                                                                                                                          ��
                                                                                               and shafts) and in the assumptions          When interpreting the results of the                                           �� �   �� �   �� �        �� �       �� �    �� �     �� �   �� �        �� �
                                          plants, giving an electricity produc-                made for the scenarios.                     model calculations, it has to be borne                                                              ������������������������������
                                          tion scenario of 192 GWe a. It was                   It can be seen that all the calculated      in mind that a whole series of phe-
                                          also assumed that only the volume                    doses lie well below the limit of 0.1       nomena that could contribute posi-
                                          of spent fuel for which contracts                    millisieverts per year (the Swiss regu-     tively to safety have not been included
                                                                                                                                                                                         Figure 7
                                                                                                                                           in the models and that many poten-            Decrease with time in toxicity of emplaced spent fuel (SF), high-level waste (HLW) and long-lived intermediate-level
                                                                                                                                           tially detrimental phenomena have             waste (ILW). The dotted green lines show the radiotoxicity of a volume of uranium ore from Cigar Lake (Canada) or La
                                                                                                                                           been treated in a simplified and              Creusaz (Canton Wallis) sufficient to fill the SF/HLW and ILW tunnels. It should be noted that the toxicity of a volume of
                                                                                                                                                                                         uranium ore is compared with the same volume of waste and backfill material. The natural radiotoxicity of a cubic
                                                                                                                                           conservative manner. The reason for
                                                                                                                                                                                         kilometre of Opalinus Clay (host rock) has, coincidentally, the same radiotoxicity as a volume of ore from La Creusaz
                              ��������������������������������������������������������                                                     excluding some favourable phenom-             sufficient to fill the tunnels.
                                                                                                                                           ena is that, at present, there are no
                    �� �
                                                                                                                                           suitable models or data for these
                    �� �
                                ��������������������������������������������������                                                         phenomena that would allow them
                    �� �                                                                                                                   to be analysed quantitatively. The
                                �������������������������������
                    �� ��                                                                                                                  existence of these phenomena is,
                               �����������������������������������������
                    �� ��                                                                                                                  however, an additional argument
     ������������




                    �� ��                                                                                                                  supporting long-term safety, particu-         bentonite that could further                                      •      Long resaturation times for the                geologically in the Zürcher Wein-
                    ��   ��
                                                                                                                                           larly where there are good prospects          reduce the effective solubility of                                       repository and its surroundings,               land possesses properties that will
                    �� ��                                                                                                                  for improving models and data in the          some radionuclides                                                       which delays the onset of corro-               result in the required degree of
                    �� ��                                                                          ���
                                                                                                                                           future – in other words it represents     •   Irreversible sorption of radionu-                                        sion and dissolution processes.                long-term safety. Safety is dem-
                                                                                                         �               ��
                                                                                                                              ��
                    ��   ��                                                                                                                a safety reserve. The phenomena in            clides in the near-field or in the                                                                                       onstrated for a wide range of cases
                                                                          ��
                    �� ��
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                                                                                                                                           question include:                             geosphere (surface mineralisation)                                 Synthesis of arguments                               that is sufficiently comprehensive
                    �� ��
                                                                                                                                          • Coprecipitation of radionuclides         •   Long-term immobilisation pro-                                      and results                                          to cover all realistically conceiv-
                        �� �                 �� �              �� �                     �� �                 �� �                  �� �       with secondary corrosion prod-             cesses in the geosphere (precipita-                                The final step in the making of the                   able paths for the future evolution
                                                                      ������������                                                             ucts of the SF, the HLW glass and         tion/coprecipitation)                                              safety case is the synthesis of all                  of the disposal system. In all cases,
                                                                                                                                               the canisters (with the exception     •   Delayed release of radionuclides                                   relevant arguments and analyses,                     the resulting radiation dose is
     Figure 6                                                                                                                                  of radium, for which coprecipita-         due to low corrosion rates of                                      including the results of the analyses                below the guideline set by the
     Evolution with time of the annual dose for the Reference Case, calculated as the sum of contributions                                     tion is considered)                       metallic ILW components (e. g.                                     of assessment cases. This synthesis                  safety authorities, in most cases
     from SF, HLW and ILW (dotted/dashed curve). The contributions of the dose-dominating radionuclides to
                                                                                                                                          • Sorption of radionuclides onto               hulls and ends), as well as a time                                 supports the following key conclu-                   by several orders of magnitude
     the curve are shown as coloured curves. The maxima of all other nuclides contained in the waste are
     below 10 -9 mSv/a.                                                                                                                        the canister corrosion products           period of complete containment                                     sions:                                               (see Fig. 5, 6).
                                                                                                                                          • Concentrations of natural iso-               by the ILW package and disposal                                   • As shown by quantitative analysis,                • The system has been shown to be
                                                                                                                                               topes in the porewater solution of        container                                                             the potential site characterised                  robust, that is to say none of the


nagra Bulletin 35

40                                                                                                                                                                                                                                                                                                                                                       41
Figure 8
Once the repository
has been backfilled
and sealed, the
landscape will be
returned to its original
“green field“ state.
The repository will
have no influence on
life at the surface, but
the whereabouts of
the radioactive
materials are known –
they are isolated
safely by engineered
barriers and suitable
rock formations.




                                                                                                                                                               Prisma




                               uncertainties regarding system          The existence of a large area of      The safety case with these conclu-
                               evolution currently identified          undisturbed host rock has been        sions supports Nagra‘s proposal to
                               would call the safety of the re-        demonstrated.                         the Swiss Government that it for-
                               pository into question.             •   The properties of the host rock       mally acknowledge that the require-
                           •   The mechanical properties of the        have been investigated in detail      ments for Project Entsorgungsnach-
                               rock at the site and the selected       in in-situ experiments at the         weis have been fulfilled n
                               engineering concept would allow         Mont Terri Rock Laboratory. The
                               the repository to be constructed,       results are in agreement with         Literature references
                               operated and, finally, backfilled and     those from the Benken borehole.       1
                                                                                                                 HSK/KSA (1993): “Guideline for Swiss Nuclear
                                                                                                                 Installations HSK-R-21/e: Protection Objectives for
                               sealed in such a way as to ensure •     The future geological evolution           the Disposal of Radioactive Waste“; Swiss Federal
                                                                                                                 Nuclear Safety Inspectorate (HSK), Federal Commis-
                               long-term safety (see Fig. 8).          of the siting region can be pre-          sion for the Safety of Nuclear Installations (KSA). HSK,
                           •   The information base for the se-        dicted fairly accurately because of       Villigen.
                                                                                                             2
                                                                                                                 Nagra (2002): “Project Opalinus Clay: Safety report.
                               lected siting region is sufficiently     the availability of numerous re-          Demonstration of disposal of spent fuel, vitrified
                                                                                                                 high-level waste and long-lived intermediate-level
                               extensive and the geological situ-      gional geological studies and be-         waste (Entsorgungsnachweis)“; Nagra Technical
                               ation sufficiently well understood       cause the general geological situ-        Report NTB 02-05. Nagra, Wettingen.

                               to support the assessment of long-      ation is comparatively simple.
                               term safety. In particular, the •       The knowledge of the properties
                               geometry and structure of the           of the waste (see Fig. 7) and the
                               host rock and the surrounding           engineered barriers is sufficiently
                               layers are well known due to a          comprehensive, being based on
                               high-resolution 3D seismic cam-         more than 20 years of scientific
                               paign and the Benken borehole.          studies in Switzerland and abroad.


nagra Bulletin 35

42                                                                                                                                                                          43
                             Nagra
Swiss National Cooperative for the
     Disposal of Radioactive Waste
Hardstrasse 73, CH-5430 Wettingen

						
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