Methodological approach to a safety analysis of radioactive waste disposal in rock salt: An example

A methodological approach was applied in preparing of the project “Preliminary Safety Analysis of the Gorleben Site” according to the German requirements for final disposal of heat generating radioactive waste. The German requirements and the approach are based on recent international documents from IAEA and OECD/NEA on safety assessment and the safety case. The approach included the description of the geological site and its future evolution coupled with a range of possible waste emplacement scenarios using site specific repository designs. The repository designs were developed to provide operational safety, long-term safety and retrievability/recoverability of the waste to comply with the German safety requirements. The German requirements require ongoing optimisation of repository designs. Analysis of the integrity, fluid flows and radiological consequences was done and the performance of the system was assessed. If the present assumptions are confirmed by future research and development, the designed repository system for drift disposal was assessed to be robust. Further optimization is possible in relation to gaseous radionuclide species for the drift disposal design and in relation to the technology of retrieval for the borehole disposal design. The site specific safety analysis identified important tasks for research and development which would have not been possible by a generic safety analysis. The methodology and safety concept can be applied to other salt rock sites and can be transferred partially to clay sites.