Failure probability of control rod insertion upon reactor scram of fast reactors

Kurisaka, Kenichi ; Naruto, Kenichi*; Sugino, Tetsu*

The failure probability of control rod insertion upon reactor scram is sensitive to the occurrence frequency of the reactor scram failure in sodium-cooled fast reactors (SFRs). The careful estimation of this probability is needed. The present study investigated the field data related to the scram demands and to their failure number. Data sources are "Joyo", "Monju", control rod drive mechanism mockup test that was performed in Japan, and PWRs in Japan and in US. Based on the investigation result, the failure probability of control rod insertion upon reactor scram was estimated for "Joyo" and "Monju" by using the hierarchical Bayes method with the Markov Chain Monte Carlo simulation. The failure probability was also estimated for a dummy reactor assuming a single success instance in rod insertion. The idea for the dummy reactor could be applied into the probability estimation of a new commercialized SFR having no operating experience.