Methods for probabilistic analyses of the containment behaviour in severe incidents and accidents

In severe incidents and accidents the containment is the ultimate barrier to keep radioactive material away from the environment. Probabilistic safety analyses (PSA) of level 2 are the tool for a systematic evaluation and quantification of the retention potential. A wide knowledge of numerous single phenomena in severe incidents and accidents is available in Germany, but up to now this knowledge has not been combined into a comprehensive level-2 PSA. Consequently there is no experience with the methodology of level-2 PSA. This report first gives some examples which allow an overview on existing foreign probabilistic containment analyses during severe incidents and accidents. The review of the scientific literature on methodologic questions concerning level 2 PSA shows that the state of the art is represented by the technique with large event trees, which has been developed and frequently applied in the USA. Additional remarks on the future practical application of this technique as well as a suggestion for the set up of an event tree for further investigations close the report. (orig.)