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| Smoke rises from the Fukushima nuclear power plant in Japan Saturday after an explosion at one of its buildings |
TOKYO — An explosion at a nuclear power plant in northern Japanon Saturday blew the roof off one building and destroyed the exterior walls of a crippled reactor, but officials said radiation leaks from the plant were receding and that a major meltdown was not imminent.
Japanese television showed a cloud of white-gray smoke from the explosion billowing up from a stricken reactor at the Fukushima Daiichi Nuclear Power Station Saturday afternoon, and officials said the threat of ongoing radiation leaks prompted them to expand the evacuation area around the facility to a 12-mile radius.
Although safety officials described the release of radioactive materials as small, they also told the International Atomic Energy Agency that they were making preparations to distribute iodine, which is used to help protect from radiation exposure, to people living near two nuclear plants that suffered damage in the quake. Japanese news media said three workers at the Daiichi plant had suffered radiation exposure.
Government officials and executives of Tokyo Electric Power, which runs the plant, gave confusing accounts of the causes of the explosion and the damage it caused. Late Saturday night, officials said that the explosion occurred in a structure housing turbines near the No. 1 reactor at the plant rather than inside the reactor itself.
The blast, apparently caused by a sharp build-up of pressure after the reactor’s cooling system failed, destroyed the concrete structure surrounding the reactor but did not collapse the critical steel container inside, they said. They said that raised the chances they could prevent the release of large amounts of radioactive material and could avoid a core meltdown at the plant.
“We’ve confirmed that the reactor container was not damaged. The explosion didn’t occur inside the reactor container. As such there was no large amount of radiation leakage outside,” Japan’s Chief Cabinet Secretary Yukio Edano said in a news conference Saturday evening. “At this point, there has been no major change to the level of radiation leakage outside, so we’d like everyone to respond calmly.”
Tokyo Electric Power, which operates the plant, which is located 160 miles north of Tokyo, now plans to fill the reactor with sea water to cool it down and reduce pressure. The process would take five to 10 hours, Mr. Edano said, expressing confidence that the operation could “prevent criticality.”
The company also said its workers also added boric acid to the containment vessel Saturday night to slow down the nuclear reaction.
Mr. Edano said radioactive materials had leaked outside the plant before the explosion, but that the explosion did not worsen the leak and that, in fact, measured levels of radioactive emission had been decreasing. He did not specify the levels of radiation involved.
Officials said even before the explosion that they had detected cesium, an indication that some of the nuclear fuel in the reactor was already damaged. That suggests that the plant experienced a partial meltdown. But officials insisted the fuel damage was contained and that the prospect of more radioactive leaks had receded.
Naoto Sekimura, a professor at Tokyo University, told NHK, Japan’s public broadcaster, that “only a small portion of the fuel has been melted. But the plant is shut down already, and being cooled down. Most of the fuel is contained in the plant case, so I would like to ask people to be calm.”
The crisis at the aging plant confronted Japan with its worst nuclear accident — and one of the biggest malfunctions at a nuclear plant since the Chernobyl nuclear disaster in 1986.
Japanese nuclear safety officials and international experts said that because of crucial design differences the release of radiation at the Fukushima plant would likely be much smaller than at Chernobyl even if the Fukushima plant had suffered a complete core meltdown, which they said it had not. But the problems at the plant are likely to increase concerns about the safety record and reliability of Japan’s extensive nuclear power facilities, which have been criticized for major safety violations in the past.
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