Host rock-specific preliminary safety concepts for the representative preliminary safety assessments

The Federal Company for Radioactive Waste Disposal (BGE) is responsible for identifying the site with the best-possible safety for the disposal of high-level radioactive waste for at least one million years in Germany. The Site Selection Procedure consists of three phases with an increasing level of detail. The first step of the first phase was completed in September 2020. Ninety sub-areas were identified that are expected to have favorable geological conditions for safe disposal. The potentially suitable sub-areas are located in three different host rocks: rock salt (halite), claystone, and crystalline rock.Representative preliminary safety assessments are one of the tools in the current phase of the Site Selection Procedure, which assess the extent to which the safe containment of radioactive waste can be expected. In this context, host rock-specific preliminary safety concepts describe how the safe containment in the disposal system is achieved. The disposal system comprises a graded system of geological (host rock and overburden) as well as engineered (backfill, sealing, canister, and waste) barriers. The key safety-relevant features of the disposal system can be summarized in the main safety functions, integrity of the barrier system and retardation of radionuclides. These safety functions are differentiated into a number of subordinate safety functions for each barrier. The interaction of the barriers and their various safety functions ensures that safe containment is achieved by the system as a whole over the assessment period.Within the preliminary safety assessments, the behavior of the disposal system is analyzed in its entirety, under consideration of possible future evolutions of the disposal system with regard to the safe containment of the radioactive waste. The safety functions provide the understanding of the safety features of the disposal system and mark the starting point for the assessment of key issues with regard to safe containment.An overview of the host rock-specific preliminary safety concepts will be provided and an insight into their barrier-specific safety functions is given. In addition, the role of the safety functions in the post-closure safety assessment will be outlined.