Feasibility demonstration for HLW disposal
Document Sample


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