Development of failure probability evaluation methodology of natural circulation heat removal function in level-1 PSA for sodium-cooled fast reactors

Yamano, Hidemasa   ; Sakai, Takaaki; Kurisaka, Kenichi 

This study is aimed to develop a methodology of failure probability evaluation for the passive safety features on natural circulation heat removal. Following the identification process on failure causes using the phenomena identification and ranking table, this paper provides a failure probability of the natural circulation heat removal function that is expected to actuate only one direct reactor auxiliary cooling system assuming the loss of two primary reactor auxiliary cooling systems. The failure probability was determined above a safety criterion of the coolant boundary temperature. The failure probability of the reference case was very low, indicating a high reliability of the natural circulation decay heat removal function.