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概要

Abstract: The 2011 off the Pacific coast of Tohoku Pacific Earthquake and the Tsunami gave the serious damage to the Fukushima-Daiichi Nuclear Power Plants (NPPs). The accidents occurred in Unit 1, 2, 3 and 4. It is said that the height of tsunami attacked Fukushima NPP was more than 14m. After 50 minutes from the automatic shut-down, tsunami attacked the NPPs in Fukushima Daiichi NPPs. For example, the Unit 1 lost A/C power caused the loss of water injection function; it made the core meltdown and unusual increase of PCV pressure in the midnight of March 11th to 12th morning. Though the Unit one has the Isolation Condenser Core Cooling system, it was stopped by the operator to keep the cooling rate of 55oC/h. Finally, the isolation signal was transmitted from the control room to the motor driven isolation valves when the control room's battery discharged. It was the initiation of the core meltdown. The lessons from the accidents, we should improve the nuclear safety regulation through the innovation of regulatory rules and safety standers. Standers and guidelines should be rules between licensees and regularly.

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