TSURUGA, Fukui Pref. – A Kansai Electric Power Co. nuclear power plant was searched Friday by the Fukui Prefectural Police for evidence of professional negligence resulting in death in connection with an accident last month.
The police said they plan to examine documents to determine officials’ responsibility for the utility’s failure to inspect a corroded coolant water pipe at the Mihama nuclear power plant for nearly 28 years until it ruptured Aug. 9, releasing superheated steam.
About 150 officers were dispatched to search the offices of Kepco and Nihon Arm Co., a Kepco affiliate overseeing maintenance of the utility’s power plants, both located inside the plant, in an operation that was likely to last through Sunday, they said.
By evening, investigators had confiscated the ruptured pipe and transported it to Fukui University, where researchers were to conduct tests on it. A different pipe section with a similar structure was also removed by police for a comparative analysis.
Kepco, the nation’s second-largest utility, said it is ready to cooperate fully with the investigation, adding that it will probe the cause of the accident on its own and make utmost efforts to prevent a recurrence.
Four workers were killed and seven others were injured in the accident. The death toll rose to five after one of the injured died Aug. 25. The workers had been doing preparation work for regular checks of the reactor.
It was Japan’s deadliest accident at a nuclear plant.
Investigations have shown that coolant water had corroded the ruptured pipe to a thickness of only 0.6 mm, compared with its original thickness of 10 mm.
Kepco has admitted the pipe had gone uninspected since the reactor went into operation in 1976.
The company is suspected of not conducting checks even after Nihon Arm notified it last November that the pipe had been missed during annual inspections, waiting about nine months until this year’s inspection, which was to begin five days after the accident.
In the wake of the accident, the Nuclear and Industrial Safety Agency under auspices of the Ministry of Economy, Trade and Industry has begun efforts to improve safety checks for pipes for secondary cooling water in nuclear reactors.