Japan’s nuclear regulator said Wednesday that the tsunami following the March 11, 2011, earthquakenot the quake itselfwas the main cause of the accident at the Fukushima Daiichi nuclear power plant.
The conclusion matters because of the implications for other nuclear-power plants. Virtually all of Japan is prone to earthquakes, but some places are relatively protected from tsunamis. Currently all of the nation’s 48 reactors are offline, and the government is weighing whether to restart some next year.
In the March 2011 nuclear accident, three reactors melted down after the plant lost main and backup power, paralyzing cooling systems.
The Nuclear Regulation Authority studied why the No.1 reactor lost backup power and concluded on Wednesday in a report that the tsunami was the main cause, based on data about temperature, pressure and other parameters. Those data were stable immediately after the earthquake hit at 2:46 p.m., suggesting the plant didn’t suffer critical damage until the arrival of the tsunami some 45 minutes later.
A previous investigation by Japan’s parliament had left more room for the possibility that the earthquake itself did significant damage.
The regulator said it would translate the report into English and post it on its website. The Japanese-language version is here.
You cannot say there was no damage by the earthquake at all. But you can say the major cause was the tsunami, looking at the data, said Tamotsu Kozaki, a nuclear engineering professor of the Hokkaido University.
Hiroaki Koide, a nuclear engineering assistant professor at Kyoto University and critic of nuclear power, said it was too early to reach a conclusion because high radiation has prevented investigators from directly checking the reactors. It seems they want to end this discussion and get away, Mr. Koide said.
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