Japan Scrambles to Avert Meltdown at Second Crippled Nuclear Reactor

TOKYO — Japanese officials took the extraordinary step on Saturday of flooding a crippled nuclear reactor with seawater in a last-ditch effort to avoid a nuclear meltdown, as the nation grappled simultaneously with its worst nuclear accident and the aftermath of its largest recorded earthquake.

On Sunday, they announced that the cooling system at a second reactor in the same aging plant had failed, forcing officials to release radioactive vapor into the atmosphere. At least 210,000 people were told to evacuate the areas.

The cooling systems at three other reactors at a second nuclear plant had also failed, officials said. While cooling might still be revived, if it could not, these reactors could also require emergency cooling, they said.

The developments — perhaps the worst involving a nuclear plant since the Chernobyl disaster 25 years ago — came as the nation struggled to recover from a devastating 8.9 magnitude quake on Friday.

For now, the most pressing concern stemmed from a radiation leak and explosion at the No. 1 reactor of the Fukushima Daiichi Nuclear Power Station on Saturday. Officials were forced to flood the overheating reactor with seawater to avoid a nuclear meltdown.

By Sunday officials were forced to take steps at another reactor — No. 3 — to avert a nuclear meltdown after a critical failure of their cooling systems briefly exposed fuel rods — a dangerous state that could lead to meltdown.

On Sunday morning, officials injected water and boric acid into the second reactor and released radioactive vapor to ease pressure, said Yukio Edano, the chief cabinet secretary. The reactor’s fuel rods had become exposed, he said, which called for the extraordinary measures.

At around the same time, radiation levels outside the plant, which had retreated overnight, shot up to 1,204 micro sievert per hour, or over twice Japan’s legal limit, Mr. Edano said.

Public broadcaster NHK flashed instructions to evacuees: close doors and windows; place a wet towel over the nose and mouth; cover up as much as possible. At a press conference, Mr. Edano called for calm. “If measures can be taken, we will be able to ensure the safety of the reactor,” he said.

The blast Saturday afternoon destroyed part of the facility, and officials said that they had filled it with sea water to prevent full meltdown of the nuclear fuel. That step would only be taken in extreme circumstances because ocean water is likely to permanently disable the reactor.

The Japanese Nuclear and Industrial safety agency said as many as 160 people may have been exposed to radiation around the plant, and Japanese news media said three workers at the facility were suffering from full-on radiation sickness.

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