Tokyo Electric Power Co. said it lost control of pressure building at three reactors at one of its nuclear power plants, and radiation levels are rising at another after a powerful earthquake shut down the plants' cooling systems.
The company is venting radioactive vapor at the Dai-Ichi plant in Fukushima, Japan, to reduce the pressure building up from steam inside the reactor containment structure, Tokyo Electric Power said in a statement. It's preparing to vent at the second plant, also. The company is monitoring radiation from the discharges.
The national government widened an evacuation order for residents who live near two of the utility's plants in Fukushima to a radius of 10 kilometers (6.2 miles) from 3 kilometers, the company said.
The radiation level in the central control room of the Dai- Ichi No. 1 reactor rose to 1,000 times higher than normal, Kyodo News reported, citing Japan's nuclear safety agency.
Temperatures in the control room at the nearby Daini plant have risen higher than 100 degrees Celsius (212 Fahrenheit), said Noaki Tsunoda, a spokesman for Tokyo Electric. Water levels to cool fuel are being "maintained," the company said in a statement.
Radiation in vapor released from the Dai-Ichi No. 1 reactor won't pose a threat to public health, Chief Cabinet Secretary Yukio Edano said at a press conference earlier today in Tokyo.
Pressure Building
The plants, 210 kilometers (130 miles) north of Tokyo, lost power after the earthquake yesterday and about 5,800 residents near the plant were ordered to evacuate. The reactors were built by General Electric Co. (GE), said Michael Tetuan, a Wilmington, North Carolina-based spokesman for Hitachi-GE Nuclear Energy, the joint venture now servicing the plants.
The Dai-Ichi facility is currently using a battery, which can last about eight hours, to run systems that keep the reactor's uranium fuel from overheating, officials of the trade ministry's Nuclear and Industrial Safety agency told reporters yesterday. Another six batteries have been secured, and the government may use military helicopters to fly them in, they said.
24 Hours
The uranium core of the reactor will stay hot for several days so water must be continually cycled through the plant to cool it, Joonhong Ahn, associate professor of nuclear engineering at the University of California at Berkeley, said in a telephone interview yesterday. If pumps cycling the water fail, the water in the core will evaporate, leading to a buildup of steam pressure, said Ahn, who taught at the University of Tokyo and visited the Fukushima nuclear complex before leaving Japan in 1995.
Reactor Meltdown
Lack of adequate cooling for a reactor may cause a core meltdown, the most dangerous kind of nuclear power accident, according to the U.S. Nuclear Regulatory Commission.
A meltdown could potentially breach a reactor's containment building, releasing massive amounts of radiation, according to information on the agency's website. The 1979 accident at the Three Mile Island reactor in Pennsylvania resulted in a partial meltdown, without a breach in the containment building, according to the commission.
"The worst thing that could happen is that the core gets exposed and starts to melt," said Robert Alvarez, a senior scholar at the Institute for Policy Studies in Washington, formerly a senior policy adviser at the U.S. Department of Energy under President Bill Clinton and a U.S. Senate staff expert on nuclear weapons.
Exactly what might happen is unknown, because no GE boiling water reactor has ever melted down, he said.
Explosions, Fires
At 700 degrees to 1,000 degrees Celsius, the zirconium metal cladding the uranium fuel would catch fire, he said. The coolant water would disintegrate into the potentially explosive elements, hydrogen and oxygen.
The 1986 Chernobyl accident in Russia caused the release of at least 5 percent of the radioactive reactor core, according to the World Nuclear Association, which represents the industry.
The 8.9-magnitude quake struck at 2:46 p.m. local time and unleashed a tsunami as high as 7 meters (33 feet), engulfing towns along the northern coast and killing hundreds. The temblor hit 130 kilometers off the coast of Sendai, north of Tokyo, at a depth of 24 kilometers, the U.S. Geological Survey said. A 7.1- magnitude aftershock followed at 4:25 p.m., it said.
GE has confirmed that its 50 employees and 30 contractors working at the plant site are safe, Tetuan said. GE-Hitachi established a 24-hour command center in North Carolina and has not been able to reach Tokyo Electric to offer help. The venture had a team working on an out-of-service reactor at the site when the first trembler struck, Tetuan said.
One person is confirmed dead at the Daini nuclear power plant, which is also also in Fukushima, said Atsushi Sugiyama, a Tokyo Electric spokesman. Two people from the Dai-Ichi plant are missing, he said.
