Active fault at Tsuruga plant not ruled out: regulator

JIJI

A crush zone under the Tsuruga nuclear power plant in Fukui Prefecture may be an active fault that would require an idled reactor there to be permanently closed, the Nuclear Regulation Authority said following its second day surveying the plant.

At a news conference Sunday, Kunihiko Shimazaki, deputy chairman of the NRA, said inspectors found a stratum deformation above crush zone D-1, which runs directly beneath the building for reactor 2.

The results of the survey, conducted by Shimazaki and four other experts commissioned by the authority, will be evaluated at a meeting Dec. 10.

If D-1 is judged to be an active fault, the regulatory group will not allow Japan Atomic Power Co. to restart the reactor.

At the evaluation meeting, regulators will listen to representatives from the utility, which claims the fault under the Tsuruga plant is inactive.

D-1 is one of the crush zones at the plant said to be at risk of shifting in tandem with the active Urazoko fault, which also lies under the plant premises.

Although there is no evidence attributing the stratum deformation to D-1, it was caused by pressure similar to what moved the Urazoko fault, Shimazaki said.

He declined to say whether the deformation took place in the past 120,000 to 130,000 years. Under Japan’s guidelines for screening the quake resistance of nuclear power plants, any fault believed to have moved on or after that time frame is regarded as active.

Nagoya University professor Yasuhiro Suzuki, a member of the experts’ team, said the inspectors agreed that there is no information at present clearly showing D-1 is an active fault. An additional survey may be needed, Suzuki said.

Shimazaki said the regulatory group will consider conducting a further survey if needed.

The Tsuruga plant is the second nuclear power station to be inspected by the Nuclear Regulation Authority for active faults, following Kansai Electric Power Co.’s Oi plant in Fukui Prefecture in November.

A conclusion has yet to be reached on whether there is an active fault at the Oil plant, with experts divided following the November survey. Reactors 3 and 4 remain online after being reactivated in July. They are the only active reactors in Japan.