More nuke plants sitting on active faults

December 11, 2012

Experts fear more nuke reactors may be sited over active faults

http://ajw.asahi.com/article/behind_news/social_affairs/AJ201212110062

THE ASAHI SHIMBUN

More nuclear power plants could be found to be sited over active fault lines as the Nuclear Regulation Authority (NRA) conducts safety reviews of facilities, experts say.

A panel of specialists with the NRA concluded on Dec. 10 that a fault line extending from below the No. 2 reactor at the Japan Atomic Power Co.’s Tsuruga plant in Tsuruga, Fukui Prefecture, is active. The reactor is likely to be decommissioned, along with the nearby No. 1 reactor.

The conclusion suggests, the experts say, that construction of some nuclear plants was approved despite insufficient data that electric companies provided or due to lax oversight of the authorities.

The Tsuruga plant is one of six sites that were ordered in August by the Nuclear and Industrial Safety Agency, the NRA predecessor, to have geological fault surveys conducted.

The authorities said that the six plants should be re-examined for possible active seismic faults in and near the facilities, saying there was not enough data showing otherwise.

The other five sites are: Kansai Electric Power Co.’s Oi plant in Fukui Prefecture; Hokuriku Electric Power Co.’s Shika plant in Ishikawa Prefecture; Kansai Electric’s Mihama plant in Fukui Prefecture; Japan Atomic Energy Agency’s Monju prototype fast breeder reactor in Fukui Prefecture; and Tohoku Electric Power Co.’s Higashidori plant in Aomori Prefecture.

Two of the four reactors at the Oi plant are the only two of the nation's 50 commercial reactors currently online.

Reactors and other crucial facilities are not allowed to be built above an active fault under the government’s 2010 quake-resistance standards for nuclear power plants.

Apart from the Tsuruga plant, many seismologists and geologists argue that a reactor at the Shika plant also sits on an active seismic fault.

There remains a sketch of a fault line extending below the No. 1 reactor at the Shika plant. It was produced by Hokuriku Electric in a geological survey when the utility applied for the installment of the reactor in 1987.

But authorities at that time determined it was not active.

Some experts, however, pointed out at a meeting of specialists at NISA in July that it was a “classic” example of an active fault.

Hokuriku Electric is conducting an additional study of the fault, but the study has been delayed.

Authorities have been reviewing existing geological data on the grounds and areas surrounding nuclear plants that were provided by the plant operators. The review was prompted by last year’s Great East Japan Earthquake, which set off a triple meltdown at the Fukushima No. 1 nuclear power plant.

An on-site inspection of the Shika plant by an NRA team is expected next year.

If the fault is assessed to be active, the No. 1 unit could be asked to be permanently shut down.

At the Mihama plant and Monju fast breeder, an active fault, Shiraki-Nyu, runs in the vicinity.

Experts say faults known to be situated underneath the reactors at the two facilities could move if the Shiraki-Nyu active fault slips.

The operators are conducting a study to come up with more data on the suspected faults.

At the Oi plant, an emergency water intake channel, which is crucial in responding to a nuclear accident, is situated above a possible active fault.

A panel of experts at the NRA conducted an on-site inspection on Nov. 2, but did not reach a conclusion.

It is expected to take months for the NRA to come to a conclusion. Additional surveys, including drilling, are expected to take place.

If a fault is found to be active, the plant must be shut down to allow work to relocate an emergency water intake channel.

But many experts say that the reactors will not need to be decommissioned simply because of that.

A separate NRA panel is expected to conduct an on-site inspection of the Higashidori plant on Dec. 13-14.

Tohoku Electric says no crucial facility sits on a fault that some specialists suspect is active.

If the fault is assessed to be active, a review of safety checks will be needed to evaluate if the plant is quake-resistant before it can be restarted.