Tohoku Electric Power, a medium-sized utility in northern Japan, said it had shut down a nuclear reactor yesterday after detecting higher-than-normal nitrogen leakage but no health risk was reported.
Onagawa Number One Nuclear Plant, some 300km north of Tokyo, was manually shut down only a week after resuming operations following a routine five-month checkup, company spokesman Satoshi Arakawa said.
"It is an unprecedented case at our company, but there has been no leakage of radioactivity," he said.
Nitrogen is routinely added to fill the reactor as a small amount continually escapes.
But an above-normal leak of nitrogen was discovered on Feb. 18.
The company had on Feb. 15 finished inspections which began on Sept. 8 of the 524,000-kilowatt boiling water reactor.
The 825,000-kilowatt Number Two Plant at Onagawa has also been shut down since Jan. 22 for a four-month routine inspection, leaving only the 825,000-kilowatt Number Three Plant in operation.
"It is not yet certain whether we will have to increase output at other plants to ensure stable electric supply to our customers," Arakawa said.
Tohoku Electric supplies power to seven northern prefectures of Japan's main island, including Miyagi, where the nuclear power plants are located, and Niigata, which was hit by a strong earthquake in October that killed 40 people.
Of the three power plants at Onagawa, the number one and two were made by Toshiba Corp and the number three by both Toshiba and Hitachi Ltd, according to Tohoku Electric.
Tohoku generates 14 percent of electricity by nuclear energy, 17 percent by hydro-electric power, 66 percent by thermal power burning fossil fuels such as coal, gas crude and oil, and the rest by a host of other sources.
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