The Yomiuri Shimbun
A cooling system at the Higashidori nuclear power plant in Higashidorimura, Aomori Prefecture, stopped temporarily after a powerful aftershock struck northeastern Japan on Thursday night, plant operator Tohoku Electric Power Co. said Friday.
According to the company, two external power sources for the Higashidori plant, which was not operating at the time due to a regular inspection, were cut off as a result of outages throughout the prefecture following the aftershock. An emergency generator was used to supply power to the plant.
The cooling system for a temporary storage pool for spent nuclear fuel rods, where all the plant's nuclear fuel was stored, stopped automatically, but restarted about one hour later.
No leakage of radioactive substances has been found, the company said. Another external power source, which was under inspection at the time of the aftershock, was restored at about 3:30 a.m. Friday.
Tokyo Electric Power Co. said Friday that the aftershock did not cause any new problems at its Fukushima No. 1 nuclear power plant. Nitrogen injections into the No. 1 reactor and the transportation of contaminated water continued smoothly despite some disturbances in restoration work, TEPCO officials said.
At Japan Nuclear Fuel Ltd.'s nuclear fuel reprocessing plant in Rokkashomura, Aomori Prefecture, two external power sources were cut off due to outages after the aftershock, but an emergency power source was activated. The plant was conducting test operations.
According to Japan Nuclear Fuel, spent nuclear fuel rods and a system to cool radioactive waste solution were unaffected.
According to the Economy, Trade and Industry Ministry's Nuclear and Industrial Safety Agency, it is extremely rare for an emergency generator or power source to be activated at a nuclear power plant.
Such systems are a last resort, meant to supply power only after regular external power sources became unusable. An emergency power source was lost at the Fukushima No. 1 nuclear power plant after tsunami ravaged the facility on March 11, making it difficult to cool down nuclear reactors in a stable manner.
Three of the four external sources for the Nos. 1 to 3 reactors at Tohoku Electric Power's Onagawa nuclear power plant in Onagawacho and Ishinomaki, Miyagi Prefecture, stopped supplying power late night Thursday. As of Friday morning, however, one of the three sources was working again, the company said.
Tohoku Electric Power is investigating the cause of the power cuts. A transformer station that supplies electricity to the plant suffered no failures.
The Onagawa nuclear power plant suspended operations after the March 11 disaster.
According to Tohoku Electric Power, the cooling systems for the temporary storage pools for spent nuclear fuel rods at the Nos. 1 to 3 reactors in the Onagawa plant stopped temporarily after the aftershock hit the area and water spilled out from each pool.
The cooling systems were manually reactivated about an hour later. The fuel rods were not exposed and no radioactive substance had been found to have leaked outside, the company said.
Tohoku Electric Power said it is possible the malfunction of a pressure gauge attached to a pump might have caused the cooling system for the No. 1 reactor's storage pool to stop. The company is investigating the reason for the temporary shutdown of the cooling systems for the Nos. 2 and 3 reactors' storage pools.
(Apr. 9, 2011)
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