3. Special Topics in Probabilistic Safety Assessments Levels 2, 3 and PSA Applications

The special topics presented in this chapter are related to the in Probabilistic Safety Assessments (PSA) level 2 (considering failure of the reactor followed by the failure of the containment) PSA level 3 (considering that there will be release to the environment), which are evaluating the risk impact on the NPP site for the workers, and, respectively, for the environment and population. Starting with level 2 PSA the increasing degree of uncertainty in assumptions makes the tasks related to the post-processing and interpretation of results of high interest. From this perspective, some aspects are presented in detail, as, for instance, the interface between the PSA assumptions and models and the general safety paradigms adopted by the international community at a certain moment in time, the use of PSA results for various applications aimed at supporting the improvements in the safety level at NPP and the use of PSA results for the decision-making process on safety aspects. The feedback to the PSA inputs is considered also important, as well as some aspects related to the research activities supporting PSA methodology.