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					     Nuclear Waste
Disposal Modelling :
    uses and needs
       at EDF R&D




  F. Dumortier (LNHE), M. Eddi
      (MFEE), S. Granet (AMA)
         Context and aims
Context
    ANDRA (French National Radioactive Waste Management Agency), in charge of the
     design and building of the repository for nuclear waste, has set out a « design
     concept 2005 », but technical options may still be modified,

    EdF, responsible for its ultimate nuclear waste, has undertaken analysis of this
     ANDRA « repository reference concept » under various technical fields in order to
     control the cost

Aims of the presentation
1.   Thermal modelling allows : the dimensioning of the repository taking into account the
     respect of thermal criterion and the optimisation of the compactness of the disposal
     installation to reduce the cost.
2.   Near Field THM modelling allows to estimate the extension of Excavation Damage
     Zone, to understand the comportment of plugs and sealings, to evaluate the Maximal
     Hydrogen pressure and its preferential pathway
3.   Long term safety assessment studies are then conducted to ensure that radiological
     impacts linked to optimized repository are low enough for different evolution scenarii.



2                 Journées scientifiques du GNR MOMAS : 23-25 Novembre
        The repository concept
Architecture : a        single horizontal level at the depth of 500 m


                            500 m




                                                               Thermal power of studied nuclear waste

                                                                                                                  Evolution of thermal power
                                                                                                                    for C2 waste package


                                                    cell                                        2400




                                                                    Thermal Power (W/package)
                                                                                                2200
                                                                                                2000

                                                 drift                                          1800
                                                                                                1600
     ANDRA source                                                                               1400
                                                                                                1200
                                                                                                1000
                                                                                                800
                                                                                                600
                                                                                                400
                                                                                                200               Selected
                                                                                                  0
                                                                                                                preliminary
                                                                                                       0   50     storage 200
                                                                                                                 100   150       250   300     350   400   450   500
                                                                                                                         Package age (years)




                                                                                                buffer to insure a better heat
                                                                                                  diffusion
                                                                 HL waste glass package
                                                                            C1 to C4 packages
3                   Journées scientifiques du GNR MOMAS : 23-25 Novembre
             Thermal modelling
        The thermal modelling allows :

        - the dimensioning that respects the
          thermal criterion of 90°C on the
                                                                                                             0m
                                                                                  Marnes du Kimméridgien




          geological barrier to prevent it from
                                                                                                             120 m

                                                                                   Calcaires oxfordiens




          any damage
                            +
                                                                            Argilites du Callovo-oxfordien   420 m


                                                                                                             550 m


        - the optimisation of the compactness
                                                                                    Calcaires du Dogger




          of the disposal installation to reduce
          the cost.
                                 +
        - the thermal profiles evolution useful for
           the other phenomena modelling


                                          Application examples :
       Cost improvement           - Stretching out the length of the tunnel (30 m -> 120 m)
         densification     - Getting longer the package storage (60 -> 90 years)
Technical improvement : reduce gas released by corrosion
                           => Reducing the steel thickness of the over-pack


   4                 Journées scientifiques du GNR MOMAS : 23-25 Novembre
    Numerical code and meshing tool
       SYRTHES (3D, transient process)
                   EDF-open source code
                  Conduction F.E.M.:
         on unstructured grids for solids
    Thermo-physical parameters and heat
      generation : f(time, space and T)
      conductivity : iso/ortho/anisotropic
                Radiation (wall to wall) :
                         all view factors




      Using    SIMAIL for meshing (parametrical            studies)

5   Journées scientifiques du GNR MOMAS : 23-25 Novembre
                                                     Modelling approach
                     Local modelling                                   Heat transfer simplified assumptions
                                                                                                   Criterion
                                     =0                                                          Tmax 90°C
              =0 Free surface Text = 10.7°C
                          =0                  0m
                                                      =0
                           Kimmeridgian                                                  Waste                  Waste
                                                                                        package                package
                                 Oxfordien
                                                                                                  Over-pack
                                                                                                  over
for ¼ cell                                                                Sleeve
  =0                                                                    (25 mm)          Clearances               Clearance
             Dy/2
                                              500                                       (Clearances ~15             (55 mm)
                                              m --
                                                                                           mm each)
                    Heat            Callovo
                    generation     Oxfordien



                                                     Px/2

                                    Dogger
               T= 78.6°C
                                             -3500 m


 ½ cell = “long term modelling” (t> 1000 ans)
 ¼ cell = “short term modelling” : to respect
                       the thermal criterion

   6                             Journées scientifiques du GNR MOMAS : 23-25 Novembre
    Improvement of numerical                                         Methodology for
          parameters                                             dimensioning optimisation
      Spatial meshing refinement                                        In 3 steps with 2 iterative loops
    Conduction : 3D- about 6*4 meshes                                      For a fixed length of cell (30m),
     (length*height for a disposal package)
                                                                        1. choose N packages (Np) per cell to
    Radiation : 2D ~similar refinement to                                 be installed => the length of buffer
           the solid meshes adopted                                        is determined (Lb)
                                                                        2. then vary the spacing (Px)
                                                                           between two cells that         Thermal
                                                                                                         optim isation
                                                                           respect the thermal
                                                                           criterion (90°C)
                                                                        3. calculate the related excavated
                                                                           volume (Vexc/package), then
                                                                           Np varies to get the minimal Vexc
                                                                            => economical optimisation :
                                                                             “best estimate dimensioning“
         Time step refinement                                                  =minimal Vexc (Np, Px)
                                                                               => “long term” modelling
Calculated (defined according to the variation
of temperature) or prescribed (by the user):
                 hours to years

7                Journées scientifiques du GNR MOMAS : 23-25 Novembre
        Next main challenges

• 3 « nested » modelling : site (km) > module(m) > local tunnel modelling
  (cm)
• More realistic modelling of the clearances (+ chemical, mechanical and
  hydraulic phenomena)
•   Taking into account saturation for argillite physical properties (porous
    media)
•   Uncertainties analysis
• Syrthes parallelization (in progress) = > smallest CPU time




8              Journées scientifiques du GNR MOMAS : 23-25 Novembre
             The near field THM modeling
Different stages in the “life” of a nuclear waste repository :

 Work stage     (2 years)
          Excavation of galleries and wells
                       Apparition of fractures and increase in permeability : EDZ

 Exploitation   stage (100 years)
          Positioning of waste containers and galleries ventilation
                       Thermal loading and water expansion

          Closing of the cells with bentonite and concrete
                       Unsaturated problem : resaturation of plugs and barriers

                       How to predict mechanical evolution of plugs and sealings

 Post   closure stage (1 million years …)
                       Thermal loading

                       Corrosion of steel pieces (production of hydrogen)

                       Evolution of EDZ due to hydrogen high pressures ?


  9                    Journées scientifiques du GNR MOMAS : 23-25 Novembre
            The near field THM modeling
Goals

 Estimation    of the Excavation Damage Zone (EDZ) around galleries and cells

 Understanding     and prediction of the comportment of sealing and plugs

 Understand     the saturation/desaturation mechanisms

 Estimate   the Hydrogen pressure and the preferential pathways

Specificities

A   fully coupled T.H.M problem on a Complex geometry

 Heterogeneous      materials with high contrasts
            Intact or damaged rock, engineered barriers (sealings, plugs, concrete), gaps between materials,
            steel (liners, jacketing, containers)

 High   contrast of initial saturation : clay initially saturated  engineered materials => stiff fronts

 Multiphysic and multiscale (time, space) problem under hydraulic specificities (high level of
capillary pressure and high level of gas pressure due to corrosion)


10                   Journées scientifiques du GNR MOMAS : 23-25 Novembre
        T.H.M coupling description
 Mechanic -> Hydraulic
          Fully saturated medium : Terzaghi relation                                                   M
                                  σ  σ  bpwI
          Partially saturated medium : Coussy formulation
                                                                                              H             T
                                               
                 σ  σ   S p   pc S dS I
                                   2 1
                                  3 Sl         
 Mechanic -> Hydraulic
        Permeability affected by damage



                       homogenisation
                                                damage                            K
                                           Practically :                           
                                                                         K    f k0 .  0 
                                                                                                3
                                                                                                    
 Thermic/Hydraulic : soft

Thermic->Mechanic (Temperatures generates dilatation effects and
mechanical stresses)

            EDF’s FE Software : Code_aster (www.code_aster .org)
  11              Journées scientifiques du GNR MOMAS : 23-25 Novembre
                      The classical two-phase flow model
 Hypothesis               :
             Porous media constituted by 2 phases (liquid + gas) et 2 components (ex. H2O et H2)
             Component mass conservation
             Darcy’s Law on each phase

 High      non linearities due to biphasic transfer term
             Diffusion term for mixture laws (Fick)

             Capillary pressure and relative permeabilities terms

                                   Example : Mualem Van-Genuchten model

                                                                                                                                   
                                                   m

                                                                                                                                                             1  Swe 1  Swe1/ m 
                     P n                                                                                                  1/ m m
                                                                                                                                     2                                               2m
   Sl  1  S wres   c   1                                                              S we 1  1  S we                                    krel 
                                                                                      l                                                              g
                                                         S wres                  k
                     Pr                                                           rel
                           
                                                                                                                              Perméabilités relatives
                                           S(Pc)
                                                                                                           1

             1                                                                                            0,9

           0,9                                                                                            0,8
           0,8                                                                                            0,7
           0,7                                                     Colis
                                                                                                          0,6
                                                                   Béton rempl.
                                                                                                                                                                      S close to 1
                                                                                                   k(S)




           0,6                                                                                            0,5
           0,5                                                     ZF
       S




                                                                                                          0,4
           0,4                                                     ZE                                     0,3
           0,3                                                     Cox                                    0,2
           0,2
           0,1                                                                                            0,1

             0                                                                                             0
                                                                                                                0       0,2          0,4         0,6    0,8       1
           0,00E+00   1,00E+08   2,00E+08    3,00E+08   4,00E+08
                                                                                                                                            S
                                 Pc (Pa)


  12                                        Journées scientifiques du GNR MOMAS : 23-25 Novembre
         Questions and perspectives reliated to
         the near field THM modeling
Physical questions :

       What happen when S close to 1 : permeabilities ? Capillary pressure ?

       Limit or validity of two-phase flow model

       Good knowledge of data in EDZ : K(e v), S(Pc)

       Effective stress/Total stress model : validity and limit (dilatant material)

Numerical questions :
       Hydraulic problem : Appearance and disappearance of a phase, stiff front treatment

       Contact problem : possible opening of gaps between plugs and rock

       Regularization methods (to avoid mesh dependency) - extension to viscoplastic model

       3D modeling : High performance computations (decomposition domain, parallelism)

       Fully coupling vs strategy of couplings between mechanic software/scheme and two -
        phase flow software/scheme




13                Journées scientifiques du GNR MOMAS : 23-25 Novembre
                 Long term safety assessment studies
Computations :
 3D modelling to evaluate hydraulic head
     array (far field)

 2D modelling around galleries containing
     waste packages : water flow + transport
     (near field)

 1D/2D convective transport in galleries /
     shafts / aquifers (different scenarii)

 Transfer in the biosphere : human dose
     limited to 0,25 mSv/year




                                                                Ingestion

         Atmosphère
                 Précipi                                                                                              Saulx
                 tation                                                          Ingestion
                                                                                               Ingestion

                            Eau de la
                                              Irrigation                                     Lait   Viande
                              nappe
                           contaminée                                                          Transfert     ANDRA source
                                 Irrigation
        Evapotrans                                                              Ingestion
         piration


              Eau du sol                                   Particules solides
                                    Transfert                    du sol




14                                             Journées scientifiques du GNR MOMAS : 23-25 Novembre
          Long term safety assessment studies
Tools :
 1D OSIRIS : transport

 2D ESTEL : water flow (saturated and non
     saturated zone) + transport (SUPG, CVFE,
     RWPT)

 3D ESTEL : water flow (saturated and non
     saturated zone) + transport (SUPG, RWPT)

On progress for 3D : MHFE + ELLAM
                                                                         500 m

     Phenomenons

 Taken into account : radiaoctive decay, sorption,
precipitation, radioactive filiation (1D Osiris)

 Not taken into account : multiphase transfers,
coupling with chemistry




15                Journées scientifiques du GNR MOMAS : 23-25 Novembre
          Long term safety assessment studies
Tools (évolution) :
 Complexification of the studies for transport
  model

           2005                                 2010                       ?
                                                                                        Transport module
          1D           2D                                    3D               3D
                    SUPG, CVFE                              SUPG          SUPG, ELLAM




 Generalization   of   use    of  domain
  decompositions and parallel computations
  (till 25 millions elements for 3D hydro
  simulations)



 Next main challenge : take into account other
  phenomena (2 phases …)



 16                Journées scientifiques du GNR MOMAS : 23-25 Novembre
         General conclusion
        Nuclear waste disposal modeling = A very complete and
                       multidisciplinary problem !
Geometry and phenomena to take into account : more an more complex
    Multiphysic
    Multiscale (space and time)
    Each phenomena has to be well understand !
A better knowledge of the physic is required
    With experimental results
Improvement of numerical tool required
 High performance computations (decomposition domain, parallelism, using of
  clusters, etc.)
 Numerical schemes adapted to each phenomena
 Uncertainties analysis
 Fully coupled schemes vs coupling of tools adapted to each phenomena ?




17                 Journées scientifiques du GNR MOMAS : 23-25 Novembre

				
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posted:12/2/2011
language:English
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