Study on preliminary level-1 PSA for Japan sodium-cooled fast reactor

Kurisaka, Kenichi 

Japan Atomic Energy Agency (JAEA) has been preliminarily applied a level-1 PSA to the safety design concept of a loop-type large scale of the Japan Sodium-cooled Fast Reactor (JSFR). As for internal initiators in power operation, typical core damage sequences (i.e., anticipated transients without scram (ATWS), loss of reactor sodium level (LORL), and protected loss of heat sink (PLOHS)) were evaluated to identify dominant failure combinations. The core damage frequency (CDF) was quantified to evaluate the adequacy of the safety design. This evaluation served to improve safety by modifying the decay heat removal system of JSFR. As part of development of reliability evaluation technology, we studied on the quantification of the sodium leak probability depending on the leak flow rate. This study serves to evaluate accident management effectiveness in the sodium-leak-related core damage sequences. As for external initiators, we conducted the seismic margin evaluation based on the seismic fragility evaluation for the principal structures and components, and confirmed that they have sufficient margin against the postulated seismic condition.