Development of Level-1 PSA method for sodium-cooled fast reactors, 1; Development plan and reactor shutdown failure event evaluation

Kurisaka, Kenichi ; Sakai, Takaaki; Yamano, Hidemasa   ; Fujita, Satoshi*; Minagawa, Keisuke*; Yamaguchi, Akira*; Takata, Takashi*

In order to evaluate the core damage frequency (CDF) of the sodium-cooled fast reactors that employ passive safety functions and seismic isolation system, the development of a level-1 PSA method was started. This study aims to provide a new evaluation method of (1) passive safety architectures related to internal events and (2) an advanced seismic isolation system related to a seismic event as a representative external event in Japan. This study reports the development plan and reactor shutdown failure event evaluation. Regarding the internal events evaluation, a quantitative analysis on the frequency of the core damage caused by reactor shutdown failure was conducted. A failure in passive reactor shutdown was taken into account in the event tree model. The failure rate of sodium-cooled fast reactor (SFR) specific components was evaluated based on the operating experience in existing SFRs by applying the Hierarchical Bayesian Method, which can consider a plant-to-plant variability. In the uncertainty analysis, we investigated a sensitivity of CDF mean value to the correlation of the probability parameters, which is quantified based on the same data source.