The Japanese government declared an “atomic power emergency” and evacuated thousands of residents living close to a nuclear plant in northern Japan after a major earthquake on Friday, but officials said there had been no radiation leak from the facility and that problems with its cooling system were not critical.

Some 3,000 people were told to leave a three-km radius around the Fukushima No. 1 plant, operated by Tokyo Electric Power and located in Fukushima Prefecture, after a mechanical failure in the cooling system, government officials said.

The evacuation was described as precautionary. Near midnight Japan time on Friday, Jiji Press, a Japanese news agency, quoted Trade Ministry officials as saying that the cooling system would be reactivated and should resume normal operations.

U.S. Air Force planes based in Japan delivered emergency coolant to the plant, Secretary of State Hillary Rodham Clinton said.

Japan relies heavily on nuclear power, and it generates just more than a third of the country's total electricity. The facilities are designed to withstand earthquakes, which are common in Japan, but experts have long expressed concerns about safety standards at the plants, particularly about the impact a major quake could have if it hit close to a reactor.

Other reactors

At least two other Japanese nuclear plants also reported trouble, but there was no radiation leak at either of them, government officials said. A number of nuclear reactors around the hardest-hit area of the country were shut down, and Japanese media said a fifth of the country's total nuclear generating capacity was offline because of the quake.

One major concern is that while operators can quickly shut down a nuclear reactor in an earthquake or another emergency, they cannot allow the cooling systems to stop working. Even after the plant's chain reaction is stopped, its fuel rods still produce heat. This is because they are filled with radioactive materials that are still throwing off subatomic particles or gamma radiation, which generates heat.

Heat from the nuclear fuel rods must be removed by water in a cooling system, but that requires power to run the pumps and to align the valves in the pipes. So the plant requires a continuous supply of electricity even after the reactor stops generating its own power.

Under control

An analyst with the World Nuclear Association, a major international nuclear power group, told Reuters that he understood fresh cool water was now being pumped into the cooling system at Fukushima, reducing the threat of a meltdown.

“We understand this situation is under control,” the analyst said, adding that he understood that a back-up battery power system had been brought online after about an hour and began pumping water back into the cooling system, where the water level had been falling.

Japanese media quoted officials in Fukushima Prefecture as saying that water levels were about 10 feet above the fuel rods at the No. 2 reactor at the plant. Tokyo Electrical Power officials confirmed that water levels had been falling but said that fuel roads had not been exposed.

Civilian power reactors are designed with emergency diesel generators to assure the ability to continue cooling even during a blackout. — New York Times News Service

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