Photo/Illutration Tokyo Electric Power Co.’s Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture (Asahi Shimbun file photo)

Shoddy welding maintenance work at the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture will push back moves to bring the facility back online by many months, perhaps longer.

The No. 7 reactor has been plagued by problems to do with installing safeguards against terrorist attacks that required further work and a new round of inspections by the Nuclear Regulation Authority, the nation's nuclear watchdog body.

TEPCO announced Dec. 24 that it had uncovered 74 instances of defective welding that is essential to safe operations of the nuclear reactor.

The utility said it had been tipped off anonymously on several occasions since March about shoddy welding work done by a subcontractor.

In its latest announcement, TEPCO acknowledged the problem and said welding would have to be redone at 1,200 or so sections, a process that will likely take until next summer.

TEPCO had intended to resume operations at the No. 7 reactor in autumn 2022, but that plan has now fallen by the wayside.

The tips about poor welding involved piping used for fire extinguishing equipment. The company in question had the job of  ensuring the piping would safely operate at 1,220 points. The utility checked 194 of them and found problems at 74, or about 40 percent.

Normally, gas is injected into the piping during welding to prevent oxidation. But the welders didn't bother to inject any gas, leaving the piping apparatus open to rapid deterioration over the long term. That, in turn, left open up the possibility of safety problems emerging because the fire extinguishing equipment might not operate properly.

TEPCO questioned 17 welders and nine admitted that they did not use gas when doing the maintenance work. One welder said he pretended to inject gas by inserting a hose into the piping, but never releasing any.

According to the report submitted Dec. 24 to TEPCO by Tokyo Energy & Systems Inc., which subcontracted the welding work to the company in question, the welders found it bothersome to lug gas canisters around and then remove them from the reactor after they had completed tasks for their shifts.

Initially, they released only a small volume of gas. Subsequently, most of the welders did not bother to use any gas at all.

Moreover, they falsified their work reports to make it appear they had carried out their tasks correctly. No supervisor from Tokyo Energy & Systems was on-site to check that the welding was being done properly. The company had only the falsified work reports as confirmation that the work had been done by the book.

TEPCO said all 1,220 points welded by the subcontractor would have to be redone. It also said that another 317 welding points undertaken by three other companies had inexpertly controlled the oxygen concentration within the piping, meaning that work will have to be redone as well.

Local authorities were incensed at the latest revelations.

Kashiwazaki Mayor Masahiro Sakurai said he strongly suspected that TEPCO and Tokyo Energy & Systems should be held legally accountable for overlooking the shoddy work at the No. 7 reactor.

“Faulty work and false reports are very serious problems,” Sakurai told reporters Dec. 24. “I have to say that there is a serious lack of awareness among those involved in the plant about the dangers to life if anything goes wrong inside a nuclear power plant.”

(This article was written by Yu Fujinami, Toshinari Takahashi and Yasuo Tomatsu.)

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