Study on precursors to accident at Fukushima Daiichi Nuclear Power Station

Watanabe, Norio

It has been recognized an important means to learn lessons from operating experience and to feed them back to the design, construction, operation and management of facilities. A lot of events involved similar occurrences which have been experienced in the past. These are referred to as precursors. In the present study, identified and discussed are the precursors to the accident at Fukushima Daiichi Nuclear Power Plant to obtain the generic lessons which should have been learned. As precursors to the Fukushima accident, six events are identified: massive internal flooding and loss of safety systems; prolonged station blackout involving loss of control room and loss of residual heat removal; external flooding involving loss of safety systems and multi units site issue; loss of offsite power with one of two emergency diesel generators inoperable; tsunami-induced flooding; common-mode loss of instrument power. Furthermore, the most notable near-miss to the Fukushima accident is discussed.