Use of PSA in pursuit of safety improvement at the Paks; NPP. Latest results and insights

Unit specific level 1 PSA models have been developed for internal initiators at full power operation of the four VVER 440-213 type reactors of the Paks NPP. Low power and shutdown operating modes of a planned refueling outage have also been included in the plant PSA, and the core damage risk due to internal fires and flooding has been quantified too. Currently seismic PSA is in progress. In addition PSA has been a useful tool to evaluate the effectiveness of the measures taken and quantify the level of safety achieved. This is accomplished by the implementation of a living PSA program. Due to the numerous plant modifications PSA models and results are updated annually. The paper summarizes the latest PSA results for the Paks NPP. Examples are given on plant improvements supported by PSA, and the effect of those improvements on the core damage risk is demonstrated. Changes in core damage risk and the main risk contributors are shown for the past few years. The main features of the living PSA program are discussed, and future plans on PSA and PSA applications for the Paks NPP are described. (author)