AESJ study on control rods withdrawal events in BWRs

In response to the government's instruction on comprehensive check of power generating facilities, a criticality incident that occurred during a periodic inspection in Shika Unit 1 reactor in 1999 was reported, which had not been reported. Criticality management is the most important task to ensure nuclear safety. This report outlines the Atomic Energy Society of Japan (AESJ)'s investigation and analysis of the unexpected control rods withdrawal events during plant shutdowns. The discussion of experts was focused on control rods withdrawal events mechanism, criticality incident analysis, safety issues, and human factors and management problems. Some proposals were included based on safety assurance and human and organizational factors. (T. Tanaka)