Seismically-induced reactor coolant leakage as an allegedly-possible cause of accident at unit 1 of Fukushima Dai-ichi Nuclear Power Station
Kukita, Yutaka; Watanabe, Norio
NAIIC emphasized the possibility of seismically-induced reactor coolant leakage and implied its causal connection to the accident, in particular at the Fukushima Daiichi Unit 1. This view of NAIIC has been addressed by the Accident Investigation Committee established by the Cabinet decision, NISA, and the Secretariat of NRA. Based on seismic response analyses, plant records and simulations, their reports uniformly note that seismically-induced leakage is unlikely to be a causal factor for the core damage though the possibility of insignificantly small leakage cannot be ruled out completely. Also refuted are some of the arguments made by NAIIC as grounds for suspecting safety-significant leakage. The present report re-examines the leak detection capability through the review of plant instruments and post-accident simulations, and adds some arguments in order to resolve the issue raised by NAIIC without technical ambiguity as far as possible. As well, the plant design uniqueness of Unit 1, the history of facility changes, the operating procedures and the actual operations are looked into to raise issues for further investigation.