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1 Simulation of the Couplex 1 test case and preliminary results of Couplex 2 H. HOTEIT 1,2, Ph. ACKERER 1, R. MOSE 1 1 IMFS STRASBOURG 2 IRISA RENNES 1. Mathematical and Numerical Models 2. Couplex 1: Final results 3. Couplex 2: Preliminary results 4. Ongoing works 1 rst Couplex Workshop, July 26-27 2001
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2 q : specific discharge (Darcy velocity [L/T]) K : permeability tensor of the porous medium [L/T] D : dispersion tensor defined by : D m : molecular diffusion coefficient [L 2 /T], I : the unit tensor [-], L, T : longitudinal and transversal dispersivity [L]. 1 rst Couplex Workshop, July 26-27 2001 MATHEMATICAL MODELS
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3 -The variable and its gradient are approximated simultaneously with the same order of convergence -The mass is conserved locally (over each element E) -They can easily handle full tensors especially for dispersion -They enforce the continuity of the fluxes across the interelement boundaries 1 rst Couplex Workshop, July 26-27 2001 NUMERICAL METHODS : Mixed Finite Element The flux is given by : RT0 basis functions defined by : j=1,...,nf A j : face (3D) or edge (2D) of E n Aj : outward normal vector to A j
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4 1 rst Couplex Workshop, July 26-27 2001 NUMERICAL METHODS : Mixed Finite Element h E : average head over E, Th Ai : average head over the face or edge i. Darcy’s law discretization with Continuity discretization Fluxes preservation
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5 1 rst Couplex Workshop, July 26-27 2001 NUMERICAL METHODS : Discontinuous Finite Element The hyperbolic part of the transport equation is solved by DFE. C is approximated by : : nodal value of C in element E, m Ei : linear basis functions, nn : number of nodes per element. Defining: the linear variation of C on edge/face A inside of E the linear variation of C on edge/face A outside of E The scheme is fully explicit and second order in time (Runge-Kutta scheme).
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6 1 rst Couplex Workshop, July 26-27 2001 NUMERICAL METHODS : Discontinuous Finite Element Step 2 : : depending on the sign of Step 1 : : the flux through A, positive if pointed outside : norm of A (length, surface).
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7 1 rst Couplex Workshop, July 26-27 2001 NUMERICAL METHODS : Discontinuous Finite Element Step 3 : stabilization with a slope limiting procedure min(i)/max (i) : min/max of over each element containing i min(E)/max (E) : min/max value of over each element which has a common node with E. E Optimization : Constraints : then Extrema :
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8 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I Main difficulties : - flatness of the domain (Lx=25000 m et Ly=695 m) ; - high hydraulic conductivity contrasts (about 10 6 ) ; - high dispersivity coef. contrasts (higher than 10 3 ) ; - high computational accuracy (C < 10 -12 with max (C SOURCE ) = 0.0015) ; - boundary conditions which generate a flow pattern which is not // to the geological structures - very long time predicition.
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9 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I : Discretization Domain discretization Quadrangular elements which respect the geological structure The element should not be too flat The mesh is refined in the neighborhood of the source The refinement is located inside a structure and not at the interface MeshN. elements N. nodes N. unknowns X Y M1 2241 2352 4592540 m3 m M2 13608 13843 27450100 m3 m M3 54432 54901109332 50 m2 m
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10 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I : Discretization Mesh M2 : NE= 1360 NN = 13843NU= 27450
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11 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I - FLOW SIMULATION Following criteria are used to study grid convergence: - head distribution - water fluxes at boundaries - pathlines and travel time with starting points at source corners - water balance for each element - dimensionless flux error defined by Double precision : Tol. PCG : 10 -14. Average MBE : 1.6 10 -11 m 3 /j Max. MBE : 1.0 10 -9 m 3 /j. Average RQmin : 64. Quadruple precision : Tol. PCG : 10 -30. Average MBE : 10 -29 m 3 /j Max. MBE : 3.10 -27 m 3 /j. Average RQmin : 10 -24 and Max RQmin 10 -20
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12 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I - FLOW SIMULATION - Head distribution and pathlines
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13 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I Vertical velocity profiles
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14 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I - FLOW Darcy ’ s velocity norm min=3 10 -9 m/y 0.01 0.001 1.e-7 1.e-6 1.e-12
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15 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I - IODE 1000 10 5 4 3 2.5 2 1.5 1 0.5 Grid Peclet number distribution :
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16 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I
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17 1 rst Couplex Workshop, July 26-27 2001 COUPLEX I
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18 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : Domain Boundary conditions : - Periodic for vertical faces - Dirichlet for horizontal faces - Fourier at alveoli (red) Simulated elements - silica - Cesium
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19 Silica Transport Model p : precipitate concentration (M/L 3 ) p : precipitation speed (L/T) p : inverse of the specific surface (L) S p : solubility (M/L 3 ) p : porosity (-) K ds : partition coefficient (L 3 /M) sol : solid density (M/L 3 ) Fourrier type boundary conditions on the glass-bentonite interface m : precipitate concentration (M/L 3 ) m : precipitation speed (L/T) S m : solubility (M/L 3 ) 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : MATHEMATICAL MODELS
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20 Cesium Transport Model m : precipitate concentration (M/L 3 ) m : precipitation speed (L/T) S m : solubility (M/L 3 ) 0 : degradation coef. (T -1 ) : porosity (-) : initial number of moles of silica Fourrier type boundary conditions on the glass-bentonite interface 1 rst Couplex Workshop, July 26-27 2001 COULEX II : MATHEMATICAL MODELS
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21 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II - Preliminary calculation Fourier type boundary conditions on the glass-bentonite interface m : precipitate concentration (M/L 3 ) m : precipitation speed (L/T) S m : solubility (M/L 3 ) Fourier type boundary conditions on the glass-bentonite interface : 10 -2 mol/m 2 /year Assumption : A1 : Cs = 0.54 mol/m 3 (saturation, instantaneous precip.) A2 : Cs = 0.099 mol/m 3 (initial concentration) A1. is reasonnable, A2. gives an underestimate of the dissolution time For one alveole : A1 : Input flux = 2.15 mol/m 2 /yearSilica dissolved after : 42 500 years A2 : Input flux = 5.54 mol/m 2 /yearSilica dissolved after : 16 500 years
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22 Cesium Transport Model 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II - Preliminary calculation Maximum concentration of Cesium : C 0 = 0.2 10 -3 mol/m 3 = 0.15 m 3 /mol Estimation of the non linearity: Inflow Assumptions: A1 : N 0 (t)=N 0 A2 : Silica flux : 5.54 10 -2 mole/m 2 /year A3 : No out-fluxes WEAK NON LINEARITY (In the buffer only) Initial number of moles of Silica : f(t) ?
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23 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II - Numerical model The retardation coefficent R is calculated from the concentration of the previous iteration step (fixed point method). Stopping criterion is based on the maximum value of the residual. It is linearly dependent on the change in the primary variables. For iteration k, the residual is defined by: Replacing x k+1 by x k + x : The residual due to the solver is defined by: Numerical strategy : Iterate until : Check if :
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24 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II - Fluxes at Fourier boundary
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25 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : CESIUM Concentration distribution at T = 100 years
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26 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : CESIUM Concentration distribution at T = 1000 years
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27 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : CESIUM Concentration distribution at T = 5000 years
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28 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : CESIUM Concentration distribution at T = 10000 years
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29 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : CESIUM Concentration distribution at T = 100000 years
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30 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : CESIUM Concentration distribution at T = 10 6 years 3D Z=cst
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31 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II - Cesium distribution Flux at lower and upper boundaries Total mass in the domain Cumulative mass balance error
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32 1 rst Couplex Workshop, July 26-27 2001 COUPLEX II : Ongoing works Ongoing works : - Extend to other nuclides - Mesh convergence study with a new elementary cell
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