Modeling approach for safety of high activity waste disposal
Christophe SERRES and François BESNUS - NUCEF 2005, Tokai Mura Japan- feb 9-10th 2005
This paper presents two examples of numerical modeling studies performed by IRSN for assessing geochemical interactions and the role of engineered barriers for the confinement of radionuclides. These examples illustrate the ability of numerical calculations to contribute to the long-term safety assessment approach. In the first example, disturbances and interactions between cementitious materials, bentonite and clayey host rock are tackled by numerical calculations at process level that enable addressing main issues of interest for performance assessment, e.g. extension and intensity of mineralogical transformations and alkaline plume spreading in the vicinity of the disposal tunnels. Once main disturbances and their effects on confinement properties of repository barriers have been identified and quantified, one may assess the role of each barrier on the overall safety of the repository for various scenarios of evolution. This assessment is tackled by integrated level calculations allowing quantifying radionuclide confinement performance of the whole repository for different stages of alteration of its components. The second example highlights the role played by bentonite engineered barriers, plugs and seals as hydraulic and migration barrier in presence of an excavation damaged zone around the vaults, drifts and shafts for different hydrogeological settings.