19 November 2002 – Kansai Electric Power Co. on Friday shut down a reactor at the Mihama nuclear power plant in Fukui Prefecture following a continued leakage of radioactive cooling water from the reactor’s container vessel since Tuesday, company officials said.
Some 5.6 tons of cooling water had leaked between the time the leak was first detected Tuesday and early Friday morning at the plant’s No 3 reactor, Fukui prefectural officials said.
The officials said the leaked water contains low levels of radioactivity and the leakage would not pose a threat to the local community. The water is accumulated inside the reactor, according to the officials.
The leak came from the primary cooling system of the 826,000-kilowatt pressurized-water reactor and engineers shut down the reactor because the leakage rate had accelerated nearly sevenfold.
Kansai Electric officials said engineers took steps to shut down the reactor when the leakage rate rose to about 400 litres per hour late Thursday, from about 60 litres per hour in the initial stage.
Company officials said the leakage, which occurred from a welded part of a reactor container valve that regulates the flow of coolant water, was detected by employees on a roving inspection of the reactor system.
The power company notified the authorities of Mihama town, the Fukui prefectural government and the central government about the trouble on Tuesday morning, but did not inform the public until the early hours of Friday, when it became necessary to shut down the reactor as workers could not fix the problem while it was in operation, the officials said.
The Fukui authorities and the central government in Tokyo did not inform the public about the situation either.
Fukui officials said they determined the situation initially did not warrant a public announcement because there were no changes in power output and no apparent influence on the reactor’s operation.
Local residents opposing nuclear power complained about the situation, saying such incidents should be made public regardless of scale.
A government agency on nuclear safety said it provisionally rated the incident as being of the lowest level in an international evaluation system. An official of the Nuclear and Industrial Safety Agency of the Ministry of Economy, Trade and Industry also said the radioactivity level of the coolant water was “quite low” because it has been filtered.
Also Friday, Kansai Electric Power said in a midterm report of its review of close to 100 occasions of voluntary inspections of nuclear power reactors conducted over the past 10 years that the inspections were carried out appropriately.
The report was presented to the national government and the Fukui prefectural government in the wake of a series of scandals involving Tokyo Electric Power Co.’s concealing of problems at its nuclear power plants.