The BASE (German Federal Office for the Safety of Nuclear Waste Management) research project Evaluation of Retrieval Concepts (BeRK) project addresses the following research questions: how could different retrievability measures and specific retrieval concepts be comparatively evaluated? How can measures for implementing and optimising retrievability be assessed in terms of their safety significance? How can trade-offs be reconstructed?

For 25 years, the rock laboratory at Mont Terri (Switzerland) has been playing an important role in the feasibility and safety studies of deep geologic radioactive waste repositories in clay formations. For the last 12 years, the Bitumen–Nitrate–Clay experiment has been running in situ experiments in this lab. This experiment addresses questions concerning the effect of biogeochemical perturbations of the clay by nitrate from radioactive waste on the migration of redox-sensitive radionuclides.

The study addresses the challenges of determining the durability of waste canisters in crystalline host rock by comparing and evaluating different international concepts for canister design and discussing their applicability to the requirements in Germany. Further focus lies on the evaluation of predominant corrosion mechanisms while also considering the geochemical environment of crystalline host rock in Germany that the canisters might be subjected to.

The METIENS project, which is carried out by the Federal Office for the Safety of Nuclear Waste Management (BASE), investigates the fundamental challenges of a site selection process that is characterized by high variability with respect to host rocks, safety concepts, and repository concepts, as in the German case. The presentation will provide examples of unavoidable subjective decisions in the evaluation of safety.