Japan Expands Evacuation Around Nuclear Plant

The power plants, known as Daiichi and Daini and operated by Tokyo Electric Power, experienced critical failures of the backup generators needed to power cooling systems after the plants were shut down, as they were during the quake.

About 45,000 people were affected by the evacuation order at the Daiichi plant, where those living within a six-mile radius were told to leave. The evacuation of the second plant was for a one-mile radius because “there is no sign that radiation has been emitted outside,” an official said.

Failure of the cooling systems allowed pressure to build up beyond the design capacity of the reactors. Small amounts of radioactive vapor were expected to be released into the atmosphere to prevent damage to the containment systems, safety officials said. They said that the levels of radiation were not large enough to threaten the health of people outside the plants, and that the evacuations had been ordered as a precaution.

Nuclear safety officials focused initially on the Daiichi plant. But by Saturday morning Japan had declared states of emergency for five reactors at the two plants, an escalation that added to worries about the safety of nuclear facilities in the quake-prone Japanese islands.

The Daiichi and Daini plants are 10 miles apart in Fukushima Prefecture, about 150 miles north of Tokyo and close to the quake’s epicenter off the coast.

The plants’ problems were described as serious but were far short of a catastrophic emergency like the partial core meltdown that occurred at the Three Mile Island plant near Harrisburg, Pa., in 1979.

A Japanese nuclear safety panel said the radiation levels were 1,000 times above normal in a reactor control room at the Daiichi plant. Some radioactive material had also seeped outside, with radiation levels near the main gate measured at eight times normal, NHK, Japan’s public broadcaster, quoted nuclear safety officials as saying.

The safety officials said there was “no immediate health hazard” to residents from the leaks, which they described as “minute,” and people were urged to stay calm.

The emergency at the Daiichi plant began shortly after the earthquake struck on Friday afternoon. Twenty hours later, the plant was operating in a battery-controlled cooling mode because the quake had knocked out the two main sources of the electrical power needed for safe shutdown.

Tokyo Electric said that by Saturday morning it had installed a mobile generator at Daiichi to ensure that the cooling system would continue operating even after reserve battery power was depleted. Even so, the company said it was considering a “controlled containment venting” in order to avoid an “uncontrolled rupture and damage” to the containment unit.

“With evacuation in place and the oceanbound wind, we can ensure the safety,” a nuclear safety official, Yukio Edano, said at a news conference early Saturday.

It was not clear, however, how long the cooling systems could continue to function in emergency mode or when normal power supplies could be restored.

Two workers were reported missing at the Daiichi plant, but the company did not explain what might have happened to them.

A pump run by steam, designed to function in the absence of electricity, was adding water to the reactor vessel, and as that water boiled off, it was being released. Such water is usually only slightly radioactive, according to nuclear experts. As long as the fuel stays covered by water, it will remain intact, and the bulk of the radioactive material will stay inside. If the fuel is exposed, it can result in a meltdown.

The reactors at the two plants shut down when the earthquake began at 2:46 p.m. Friday. As designed, emergency diesel generators were started up to provide power for continued operations of the cooling functions.

• 1
• 2

Next Page »

Ken Belson contributed reporting from New York.

via nytimes.com