Systems importance analysis in the probabilistic safety study on the Italian reference PWR

The Probabilistic Safety Study (PSS) on the Italian reference PWR, or Progetto Unificato Nazionale (PUN) (1), was carried out on the basis of the plant conceptual design, with the main goals of (2): providing an assessment of core damage frequency for the PUN design and validating the conceptual design, developing a living level 1 PRA model which could be used during the plant design and operation to evaluate the impact of design changes and regulatory requirements, formatting and sorting the results such that the expansion into level 2 or level 3 PRA analysis would be totally compatible with the level 1 analysis. The approach to the importance analysis and the main results are discussed. (orig./HSCH)