Japan warns of radiation leak from quake-hit plant

Japan warned of a possible radiation leak as authorities battled to contain rising pressure at two nuclear plants damaged by a massive earthquake, and were moving tens of thousands of residents in the area out of harm's way.

Tokyo Electric Power Co said it has begun steps to release pressure at its two nuclear power plants in Fukushima, located some 240 km (150 miles) north of Tokyo.

While some radiation leakage could be expected, Naoto Sekimura, a professor at the University of Tokyo, said a major radioactive disaster was not likely.

"No Chernobyl is possible at a light water reactor. Loss of coolant means a temperature rise, but it also will stop the reaction," he said.

"Even in the worst-case scenario, that would mean some radioactive leakage and equipment damage, but not an explosion. If venting is done carefully, there will be little leakage. Certainly not beyond the 3 km radius."

Kyodo news agency reported that authorities had begun evacuating about 20,000 people from the vicinity of one of the plants, the Daini plant. Prime Minister Naoto Kan, who was flying by helicopter to view the plant by air, had earlier ordered that residents within a 10 km radius to be evacuated from the other plant, the Daiichi plant.

Chief Cabinet Secretary Yukio Edano said amount of leaked radiation would likely be small.

"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," he told a news conference.

TEPCO said it had lost ability to control pressure in some of the reactors at its Daini plant as it had with the Daiichi plant. Pressure was stable inside the reactors of the Daini plant but rising in the containment vessels, a spokesman said.

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 US 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.

Toshiaki Sakai, director of the Japan Atomic Industrial Forum International Cooperation Center, said global nuclear power companies around the globe have since the US accident implemented over 53 safety improvements to avert a repeat.

Japan informed the International Atomic Energy Agency (IAEA) 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 reactors shut down due to the earthquake account for 18 percent of Japan's nuclear power generating capacity.

Nuclear power produces about 30 percent 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 percent 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.