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Japan warns of small radiation leak from quake-hit plant

Posted On: Mar. 11, 2011 12:00 AM CST

TOKYO (Reuters)—Japan warned there could be a small radiation leak from a nuclear reactor whose cooling system was knocked out by Friday's massive earthquake, but thousands of residents in the area had already been moved out of harm's way.

Underscoring grave concerns about the Fukushima plant some 150 miles north of Tokyo, U.S. Secretary of State Hillary Clinton said the U.S. air force had delivered coolant to avert a rise in the temperature of the facility's nuclear rods.

Pressure building in the reactor was set to be released soon, a move that could result in a radiation leak, officials said. Some 3,000 people who live within a 2-mile radius of the plant had been evacuated, Kyodo news agency said.

"It's possible that radioactive material in the reactor vessel could leak outside but the amount is expected to be small and the wind blowing towards the sea will be considered," Chief Cabinet Secretary Yukio Edano told a news conference.

"Residents are safe after those within a 3 km radius were evacuated and those within a 10 km radius are staying indoors, so we want people to be calm," he added.

Prime Minister Naoto Kan was set to visit the plant on Saturday morning and also fly over the quake-hit area.

Tokyo Electric Power Co said pressure had built up inside a reactor at the Fukushima-Daiichi plant after the cooling system was damaged by the earthquake, the largest on record in Japan.

Pressure may have risen to 2.1 times the designed capacity, the trade ministry said. Media also said the radiation level was rising in the turbine building.

The cooling problems at the Japanese plant raised fears of a repeat of 1979's Three Mile Island accident, the most serious in the history of the U.S. nuclear power industry. However, experts said the situation was, so far, less serious.

Equipment malfunctions, design problems and human error led to a partial meltdown of the reactor core at the Three Mile Island plant, but only minute amounts of dangerous radioactive gases were released.

"The situation is still several stages away from Three Mile Island when the reactor container ceased to function as it should," said Tomoko Murakami, leader of the nuclear energy group at Japan's Institute of Energy Economics.

Japan informed the International Atomic Energy Agency that the quake and tsunami cut the supply of off-site power to the plant and diesel generators intended to provide back-up electricity to the cooling system.

The Union of Concerned Scientists, a U.S.-based nonprofit organisation, said this power failure resulted in one of the most serious conditions that can affect a nuclear plant—a station blackout—during which off-site power and on-site emergency alternating current (AC) power is lost.

Nuclear plants generally need AC power to operate the motors, valves and instruments that control the systems that provide cooling water to the radioactive core. If all AC power is lost, the options to cool the core are limited.

Power supply systems that would provide emergency electricity for the plant were being put in place, the World Nuclear Association said, with a source in the organisation saying "the situation is improving."

The reactors shut down due to the earthquake account for 18% of Japan's nuclear power generating capacity.

Nuclear power produces about 30% of the country's electricity. Many reactors are located in earthquake-prone zones such as Fukushima and Fukui on the coast.

The IAEA estimates that around 20% of nuclear reactors around the world are currently operating in areas of significant seismic activity.

It said the sector began putting more emphasis on external hazards after an earthquake hit TEPCO's Kashiwazaki-Kariwa plant in July 2007, until then the largest to ever affect a nuclear facility.

When the earthquake hit the Kashiwazaki-Kariwa nuclear power plant four reactors shut down automatically. Water containing radioactive material was released into the sea, but without an adverse effect on human health or the environment, it said.

TEPCO had been operating three out of six reactors at the Fukushima Daiichi nuclear plant at the time of the quake, all of which shut down.

A spokesman said that there were no concerns of a water leak for the remaining three reactors at the plant, which had been shut for planned maintenance.