Criteria for assessment of results from level 2 PSA

Probabilistic criteria are used to judge the acceptability of PSA results. Highest level criteria set limits to acceptable societal risk, which requires performance of level 3 PSA. In many countries - including e.g. Finland and Sweden - performance of level 3 PSA is not required, and probabilistic decision criteria (limits or targets) are defined only at core damage frequency and large release frequency level. The definition of probabilistic criteria for level 2 PSA has been one of the key issues discussed in the Nordic study on validation of safety goals. There is a need to discuss and define more precisely the decision criteria related to unacceptable releases, as they seem to be understood differently in different organizations. For instance, the inclusion or exclusion of long-term effects makes a big difference as well as the inclusion or exclusion of the affected population in neighboring countries. This paper presents the summary and conclusions from the Nordic study with respect to probabilistic criteria for level 2 PSA. In addition, the interpretation of the release criteria (<100 TBq, Cesium-137) defined in the Finnish regulatory guide YVL 2.8 will be presented by means of off-site consequences. Such assessments of the environmental consequences can be used as references to validate safety goals related to CDF and large releases as surrogates of societal risk.