TOKYO — Experts judged on Wednesday that a reactor on Japan's west coast is located on ground at high risk of an earthquake, setting in motion a process that will likely lead to the first permanent shutdown of a nuclear plant since the 2011 Fukushima crisis.
Mothballing the reactor at Japan's oldest nuclear station would be the most stringent measure adopted in Japan since the meltdowns at the Fukushima Daiichi nuclear station north of Tokyo exposed failings in nuclear oversight.
All 50 reactors in the country were closed down for checks and only two have since been brought back on stream.
Reactors at five other nuclear stations are under review over the possibility they also sit on active faults.
A panel of seismologists advising the Nuclear Regulation Authority (NRA) issued their assessment that a fault known as D-1 under the Tsuruga nuclear plant on Japan's west coast is active. This paves the way for NRA to rule that the station is too risky to operate.
"Erring on the side of safety, we believe the D-1 faultline is active," the panel concluded in its report.
"Safety levels [at Tsuruga] have been low and it is really just a matter of luck that there hasn't been an accident," Kunihiko Shimazaki, the head of the panel, said after the report was finalized. "We are taking the first steps to correct the situation."
Japan Atomic Power Co., which operates the two-reactor Tsuruga station, had no immediate comment. Previously it has said the fault is not active.
The determination that Tsuruga is built on an active fault puts the plant in breach of nuclear station siting guidelines set by the government.
While the NRA does not have legal authority to order a permanent shutdown, its chairman, Shunichi Tanaka, said in December the watchdog would not allow the Tsuruga No. 2 unit to restart, should the fault be found to be active.
The NRA was set up in September last year to replace a regulator that was widely criticized for being too close to the industry it was supposed to oversee.
The NRA's commission is expected to endorse the findings on Tsuruga as early as next Wednesday and decide what action to take when its new regulations on reactors go into effect in July.
Those regulations would make the current guidance that nuclear stations cannot be built over active faultlines legally enforceable.
Japan is one of the world's most seismically active countries. An earthquake and tsunami in March 2011 caused three reactor meltdowns at the Fukushima plant, the worst nuclear disaster in 25 years.
Utilities have had to boost imports of fossil fuels to cover the shortfall in generation from nuclear plants, pushing the world's third-biggest economy into a record trade deficit.
Tsuruga's No. 2 unit has 1,160-megawatts of capacity and is located next to the 357 megawatt No. 1 unit, Japan's oldest reactor.
That reactor, also under review over a possible active faultline, may also have to be mothballed as it is more than 40 years old, the lifetime limit for operations under policy introduced since Fukushima.
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