Challenge. Provide characterization data and analyses to support selection of a suitable site for the safe geologic disposal of radioactive wastes.

Solution. As part of Andra’s efforts to characterize potentially suitable sites and rock types (granitic and crystalline, clay-rich sedimentary, and marl deposits were being considered) for the geologic disposal of radioactive wastes, the potential host repository formations were drilled, cored, and tested at each site to establish hydrogeologic properties. INTERA designed and performed pumping and straddle-packer tests, interpreted the tests using the INTERA-developed well-test simulator, GTFM (the code was later enhanced and renamed nSights), and conducted sensitivity and confidence analysis of the test results. Based on the characterization results, a clay site at Bure was selected for the construction of an underground research laboratory (called the Meuse/Haute-Marne Underground Research Laboratory [URL]) for more detailed characterization and testing. In support of testing in the Meuse/Haute-Marne URL, INTERA has interpreted hydraulic tests performed in the Callovo-Oxfordian argillites. The very low hydraulic conductivity of these clays requires specific packer testing techniques including pulse or constant injection rate tests. We used nSights to interpret these tests, applying the built-in automatic calibration tools on both Cartesian and normalized data. Each test interpretation included a comprehensive sensitivity analysis. We also provided training to Andra hydrogeologists on specialized well test analysis techniques and the use of nSights. INTERA has also developed and applied numerical models to evaluate processes important to the long-term performance of a proposed repository at Bure. This includes simulating the migration of gas from the low-permeability clay host rock into the overlying, higher-permeable carbonate rock units, and evaluating the migration of radionuclides within the waste disposal modules, their seals, and the near-field argillites resulting from the degradation of ILW packages in the alkaline anaerobic conditions of storage.