Research and development with the trio-ef code for the performance assessment of French high level waste repositories

The law relative to radioactive waste management voted in December 1991 by the French National Assembly and the Fundamental Safety Rule set the framework for the performance assessments that will be produced within the 13 year period of experimental programs heavily relying on the underground laboratories. The performance assessment (P.A.) methodology is based on the development of two types of models: - A global P.A. tool based on the linkage of simplified P.A. models which simulate the release of radionuclides and calculate their impact for the different host rocks and selected scenarios. These models take into account the existing uncertainty in adequate geosphere representation and parameter values and are validated against detailed phenomenological models. - Specific phenomenological models which describe in detail the physical and chemical mechanisms likely to influence the radionuclide migration. According to the respective importance of these mechanisms the corresponding models may be integrated in the P.A. code. These models are developed in order to prepare the experiments which will be performed in the underground laboratories, to analyze important coupling phenomena and to validate the hypothesis made in the P.A. models. As part of the work done at the CEA/DMT both phenomenological and P.A models may take advantage of the computational environment of TRIO-EF code which allow to represent complex geological media in a convivial manner. For reference calculations P.A. models are utilized directly. For multiparameter sensitivity analysis, in order to alleviate computer time constraints and increase the versatility, it is planned to develop simplified models validated against P.A. models. (author). 13 refs., 2 figs