Abstract
The Fukushima Daiichi Nuclear Power Plant, resulting from a massive earthquake, had the worst accident. Its causes are studied from safety culture and the inherent safety points of view. The matters that these fundamentals had not been embodied in the nuclear plants are as follows: priority of safety, seismic strengthening works, redundancy and diversity of subsystems, asymmetry failure mode; simplification and limitation of baneful effects on reactor cooling system, simplification of reactor building, attenuation and avoiding knock-on effect by miniaturizing reactor, tolerance toward leakage or melt-down at reactor pressure vessel, tolerance toward hydrogen gas generation, limitation of gas explosion effects, simplification of emergency countermeasures, and making status clear in emergencies. Therefore, the accident was triggered by the earthquake, but the escalation into an extremely significant accident was directly caused by a lack of safety principle and inherent safety designs. It must be more man-made than natural disaster.
