Modelling an underground waste disposal site: Scaling up the source terms and numerical simulations
A. Bourgeat1, I. Boursier1,2, O. Gipouloux1
 
1 Institut Camille Jordan UMR 5208 U.Lyon1-CNRS
15Bd Latarjet 69622 Villeurbanne, France
2 ANDRA
1,7 rue Jean Monnet 92298 Chatenay Malabry, France


The study of nuclear waste storage in a deep geological medium is at present an important challenge, especially for high level, long lived radio-elements. In particular, numerous numerical simulations are necessary for performance assessment or safety analysis processes. Due to the large scale of the study domain, direct numerical simulations based on a microscopic scale are then not realistic. The global behaviour of a such underground radioactive waste disposal is modelized by homogenisation of the source terms in [1]. This model is usefull for computations involved in safety analysis. A second model (more precise in the vicinity of the storage), obtained by a first order matched asymptotic expansion, is also studied in [1].

Both models are checked numerically with an engineering tool on a test case defined by Andra. A classical advection-diffusion model is used in a three layer domain: a low permeability host layer (containing the storage) embeded between two higher permeability layers. In case where the host rocks are supposed to have same diffusion coefficient, we obtain good results for the homogenized models according to fine scale simulations. But, in case of high contrast of the diffusion of the host rocks, the host layer diffusion coefficient disappear in the homogenized model, and then results are then not so good as before. Then a new rescaling is suggested, taking into account the diffuison contrast. By this way, numerical results for homogenized models are in agrement with the fine scale simulations.

References

[1]
A. Bourgeat, O. Gipouloux, E. Marusic-Paloka. Modelling of an underground waste disposal site by upscaling, Math. Meth. in Appl. Sci., 2004.
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