Uncertainty of the level 2 PSA for NPP PAKS

In the Level 1 PSA for internal initiators and internal hazards of Paks NPP 60 initiating events starting from nominal power operation were studied and over 500 sequences were found to lead to 'core damage' end state. As the Level 2 PSA is based on the Level 1 PSA, Level 2 PSA also covers all the internal technological events occurring at nominal power and shut down states and also the influence of fire and flooding at nominal power. This paper is a short summary of the uncertainty analyses performed so far within the level 2 PSA for NPP Paks. Some important analysis steps and methods are highlighted with examples of results obtained. The uncertainty in containment failure state frequencies for NPP Paks is in the focus of attention in this paper. (authors)