OSAKA–Kansai Electric Power Co. said Saturday it would halt the operation of a nuclear reactor at its Oi power plant in Oicho, Fukui Prefecture, due to a problem with a tank used to store water for emergency reactor-cooling functions.
The reactor’s shutdown could negatively impact the reliability of the electricity supply in the Kansai region.
According to the utility, pressure inside a tank containing water mixed with boric acid–a solution used to inhibit nuclear fission reaction–decreased at about 10:45 p.m. Friday.
The incident did not violate the power company’s safety standards, because the pressure returned to a normal level within an hour, but Kansai Electric said it decided to stop operations at the plant’s No. 1 reactor to investigate the cause of the pressure dip.
The company said it planned to shut the reactor down at about 9 p.m. Saturday.
The tank is part of the reactor’s emergency core-cooling system. If the amount of coolant liquid in the reactor was to fall below a certain level–because of damage to a water pipe, for instance–the water-boric acid solution inside the tank would be automatically released to help cool down the reactor.
The No. 1 reactor, which has a power-generation capacity of 1,175 megawatts, had been undergoing the last phase of regular scheduled inspections. That stage involves checking the reactor’s equipment during operation, after which the Nuclear and Industrial Safety Agency conducts an absolutely final inspection.
The reactor resumed operations on March 10, the day before the Great East Japan Earthquake and ensuing tsunami.
Usually, the nuclear safety agency’s final inspection takes place within a month of a reactor being restarted. However, Kansai Electric has not lodged an application with the agency, as the firm has been preoccupied with preparing new safety measures since the March 11 disaster.
Thus, the reactor has been operating at full capacity for more than four months without having been assessed by the safety agency.
There is no telling when Kansai Electric might be able to restart the No. 1 reactor again. Once its investigation into the cause of the problem with the tank is complete, the firm will need approval from the Fukui prefectural government to restart the reactor.
A spokesman for the power company said: “It’s uncertain whether we’ll be able to get approval to resume operations at the power plant after the reactor has been shut down. We can’t even guess when operations might resume.”
A Fukui prefectural government nuclear power official said: “I don’t think that just finding the cause of the trouble at [Oi power plant’s No. 1] reactor will make it possible to resume operations. We’ve expressed this opinion to Kansai Electric.”
Fukui Gov. Issei Nishikawa has previously indicated he will not permit the restart of idle nuclear reactors until the central government has established new safety standards.
Kansai Electric has 11 nuclear reactors, all of them located in Fukui Prefecture. Operations at four had already been halted before Friday’s incident at the Oi plant, and another two are scheduled to be shut down over Thursday and Friday for scheduled inspections.
Halting the Oi power plant’s No. 1 reactor will lower Kansai Electric’s supply capacity to 30,480 megawatts. That figure will further drop to 29,820 megawatts by Friday.
With 13 commercial nuclear reactors in total–two owned by the Japan Atomic Power Co.–Fukui Prefecture has the most of any prefecture in the nation.