Assessment of the interdependencies between the safe construction and operation of a repository for high-level radioactive waste and long-term safety. Synthesis of the results from the BASEL project

The interaction between the post-closure safety and the operational safety has become of vital importance for the safety assessment of geological disposal facilities. The numerous links between pre- and post-closure arguments of the safety case call for a methodology to analyse and document the relationships and to determine the conditions of the repository at the time of closure, which form the basis of the demonstration that the facility is safe over the long term. In the German R&D project BASEL the interactions between pre- and post-closure phase were analyzed by a FEP analysis. Therefore, a FEP catalogue for the operational phase was developed based on generic technical disposal concepts for repositories in clay, crystalline and salt rock. The FEP catalogue was then used to derive internal hazards for the operational phase and discuss appropriate potential prevention and mitigation measures and their influence on long-term safety. The objectives of the R&D project BASEL were triggered by discussions from the international activities of BGE TECHNOLOGY and GRS in the Integration Group for the Safety Case and the Expert Group on Operational Safety of the OECD/NEA, as well as the GEOSAF project of the IAEA. For the past four years there has been an intensive exchange with these activities in the course of the BASEL project. Annex B provides a detailed English summary of the results, including a translation of the FEP and derived internal hazards, in order to make the results of the BASEL project available internationally.