Faults under Shika N-Power Plant Not Active: NRA

Yomiuri file photo
Shika nuclear power plant

TOKYO — The Nuclear Regulation Authority decided Friday that there are no active faults underneath Hokuriku Electric Power Co.’s Shika nuclear power plant, overturning a view presented by an expert panel in the past.

At a review meeting, the nuclear watchdog broadly accepted Hokuriku Electric’s view that none of the faults underneath the plant in the town of Shika, Ishikawa Prefecture, are active.

An NRA expert investigation team suggested in 2016 that some of the faults may be active.

Hokuriku Electric applied for a screening of the Shika plant’s No. 2 reactor under new stricter safety standards in August 2014. In April 2016, the agency’s expert team said that there was a possibility that the S-1 fault underneath the reactor building of the No. 1 reactor and the S-6 fault underneath the pipes carrying coolant seawater to the No. 2 reactor could be active.

Meanwhile, the team asked for more data, saying that resources were lacking.

The power utility conducted borehole investigations at a total of 420 locations. It analyzed 10 faults, examining the ages of mineral veins crossing through the faults in addition to those of the strata on top of them. It concluded that none of the faults were “active faults with possibilities of moving in the future.”

Akira Ishiwatari, the NRA commissioner in charge of screenings, said at Friday’s review meeting that “many pieces of evidence were gathered to determine [that the faults were not active] as a result of the reevaulation using large amounts of data,” finding Hokuriku Electric’s view valid.

Under the NRA’s new regulatory standards, safety-critical buildings such as reactor buildings cannot be built on active faults that may move in the future. The new standards were introduced after the March 2011 meltdowns at Tokyo Electric Power Company Holdings Inc.’s Fukushima No. 1 nuclear plant caused by a massive earthquake and tsunami.

Active faults are defined as faults for which activity since 120,000 to 130,000 years ago cannot be ruled out.

Hokuriku Electric described the NRA’s decision as a “big step forward in the screening process toward the restart of operations,” as it will lead to a sense of safety among locals.