TSURUGA, Fukui Pref. – Kansai Electric Power Co. admitted Tuesday it failed to check a reactor pipe in its Mihama nuclear plant in Fukui Prefecture that burst and scalded four workers to death with steam, even though it knew for months that it needed inspection.
The steam leak from the carbon steel pipe at Mihama’s No. 3 reactor Monday afternoon also injured seven other workers. The pipe had not been changed in 27 years of operation.
It was Japan’s worst nuclear plant accident in terms of the death toll, but there was no radiation leak.
Fukui Prefectural Police are looking for evidence that the nation’s second-largest utility committed professional negligence resulting in death and injury, investigative sources said.
Kepco said after the accident that it found a hole in the 56-cm-diameter pipe that sends pressurized steam in the turbine facility.
It said steam erupted from the ceiling of the second floor, onto the 11 victims.
According to the sources, the section of pipe that was damaged should have been part of an earlier inspection but was excluded due to a Kepco error.
The utility was notified of the mistake by Nihon Arm Co., a subcontractor that services its power plants, in November, but did nothing about it, the sources said.
The sources said that although Nihon Arm noticed the omission in April, it did not immediately tell Kepco. Nihon Arm meanwhile says its staff informed Kepco in April.
Investigators said the thickness of the burst pipe is normally 10 mm, but it had been worn down to 1.4 mm in some places, most likely due to the swirling of the coolant water inside.
Operators are required to change the pipes before their thickness erodes to 4.7 mm. But Kepco had not conducted any ultrasound inspections to check pipe thickness since the No. 3 reactor began operations in December 1976.
After visiting the site, Shoichi Nakagawa, minister of economy, trade and industry, told a news conference: “To put it flatly, (the damaged pipe) was extremely thin. It looked terrible, even to a layman.”
Nakagawa, who is in charge of administrative measures to ensure the safety of nuclear power, also apologized to local residents.
Kepco inspected other facilities and replaced the pipes at the Takahama Nuclear Power Plant’s No. 3 reactor and Oi Nuclear Power Plant’s No. 1 reactor, both in Fukui Prefecture, with stainless steel ones between 1998 and 2003 because they had worn so thin that they would not last another two years, the sources said.
Kepco said Tuesday that it will shut down its other nuclear reactors for inspection if there are any major items that had not been checked.
Police also suspect that Kepco violated safety regulations stipulating the complete shutdown of reactors for annual checks when it had more than 200 workers move in inspection equipment while the reactor was still running, the sources said.
They suspect the utility tried to cut costs by keeping the reactor in operation until the last possible minute before the inspection, which was to start Friday.
Kepco officials said large numbers of workers are often inside reactor facilities during preparations for annual inspections but claimed there is no legal problem with the practice.
If it is proved that negligence took place, the accident will further heighten public distrust in the country’s nuclear power industry, which has been rocked by accidents and scandals, including utilities covering up safety violations and reactor defects.
The Nuclear and Industrial Safety Agency on Tuesday instructed four utilities that operate similar pressurized-water reactors to check their facilities.
Kepco President Yosaku Fuji visited hospitals Tuesday where the injured were being treated and met with relatives of the deceased.
Although he apologized to the families for the accident, Fuji said they told him the fiasco was “not something that can be laid to rest by an apology.”
Masao Takatori, uncle of 29-year-old Hiroya Takatori, one of the four killed, said he felt anger and bitterness over his nephew’s death.
“He was frothing at the mouth — I couldn’t bear to look at the body,” he said, adding that the victim’s parents stayed with the body throughout the night.
Kazuo Nakagawa, a cousin of 41-year-old Kazutoshi Nakagawa, who also died, noted that there are many in his neighborhood who work in the nuclear power industry.
Kazutoshi “often said his job wasn’t dangerous,” he said. “We’ve lost a good family man.”