Evaluation of the influence of various parameters on a clay barrier resaturation in isothermal conditions
Résumé
Many projects of high level waste repositories in geological media involve an engineered clay barrier, placed between the waste and the surrounding host rock. By hydrating progressively on contact with the interstitial water, the barrier swells, seals the gaps, and then provides a global mechanical stability of the waste - clay barrier - host rock system.
In a high-level radioactive waste repository, the thermal waste creates a thermal field in the vicinity of the waste. The maximum admissible temperature for the barrier (beyond which physical, mechanical or chemical properties break down) dictates the distance between the canister cells and consequently the size of the repository. Thus a precise assessment of this criterion is a matter of great importance.
The study is focused on the hydraulic behaviour of the barrier. A storage cell containing one high level radioactive waste canister is simulated for the East of France repository site. A cylindrical geometry, composed of a barrier layer surrounded by a site layer, is computed with the code CASTEM2000.
Initially, the site is saturated whereas the barrier is partially unsaturated. Neglecting the initial ventilation phase in the repository site, we suppose that the barrier is in thermal equilibrium with the surrounding site. Their average temperature is 50$^o$C.
The models implemented in the CASTEM code are based on the mixed-hybrid finite element formulation. The numerical model used for this computation
supposes that air remains at a constant pressure and water only exists in a liquid state.
This paper is devoted to the analysis of the barrier resaturation by the site water. The parametric study concerns the influence on the resaturation time of the clay material, the boundary conditions on the external site limit, the air pressure and the taking into account of the gravity. The results are the pressure and the saturation versus time.
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