Experts call for more studies on fault at Japan’s only active nuclear plant

November 05, 2012

THE ASAHI SHIMBUN

Japan’s new nuclear watchdog remained split over whether an active fault runs underneath emergency equipment at a nuclear power plant, delaying a decision on the fate of the nation’s only running reactors.

A team of five experts under the Nuclear Regulation Authority will meet again on Nov. 7 to delve further into the issue. But many of them said at a meeting on Nov. 4 that new studies are necessary before any conclusion is reached.

NRA Chairman Shunichi Tanaka has said the nuclear watchdog will ask Kansai Electric Power Co. to shut down its Oi nuclear plant in Fukui Prefecture if the fault running beneath the facility is confirmed, or strongly suspected, as active.

The experts on Nov. 2 inspected two locations at the Oi plant where Kansai Electric had exposed geological formations.

They agreed that geological formations at one location appeared to have slid during the past 125,000 years, but they were divided over whether this was caused by an active fault or by a landslide.

They could only reach a broad agreement that there was no clear evidence to rule out the possibility that the fault in question, called the F-6 fracture zone, is active.

Under government quake-resistance guidelines, a fault is defined as active if there are signs that it moved during the past 120,000 to 130,000 years.

NRA Deputy Chairman Kunihiko Shimazaki said Nov. 2 that the agency may ask Kansai Electric to conduct additional investigations.

The plant’s No. 3 and No. 4 reactors are the only ones in Japan that have been restarted since the meltdowns at the Fukushima No. 1 nuclear plant last year. Kansai Electric and other utilities have been urging the government to approve the resumption of operations at additional reactors.

At the Nov. 4 meeting, team member Mitsuhisa Watanabe, a professor of geomorphology at Toyo University, called for immediately shutting down the Oi plant, saying the survey confirmed the F-6 fracture zone as active.

“An active fault runs directly under important equipment,” said Watanabe, who has previously warned about the risks of an active fault at the plant. “It is not necessary to argue that a conclusion is premature.”

An emergency water intake channel, which receives seawater to cool emergency diesel generators, runs directly above the F-6 fracture zone.

Under government guidelines, key components of a nuclear power plant cannot be built directly above an active fault.

But other experts on the team said a single survey and the limited data available were not enough to declare the F-6 fracture zone as active.

“Geological formations could slip as a result of a landslide,” said Atsumasa Okada, a professor of active fault studies at Ritsumeikan University. “(The shift) appears to have been caused more by a landslide (than by an active fault).”

Daisuke Hirouchi, an associate professor of geography at Shinshu University, said they could not rule out the possibility that it is an active fault.

Norio Shigematsu, a senior research scientist at the National Institute of Advanced Industrial Science and Technology, meanwhile, cited the possibility that it is not an active fault.

THE ASAHI SHIMBUN
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Experts discuss the results of a fault survey at the Oi nuclear power plant on Nov. 4. (Toshiyuki Hayashi)

Experts discuss the results of a fault survey at the Oi nuclear power plant on Nov. 4. (Toshiyuki Hayashi)

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  • Experts discuss the results of a fault survey at the Oi nuclear power plant on Nov. 4. (Toshiyuki Hayashi)
  • At the Oi nuclear power plant, experts inspected two exposed geological formations on Nov. 2, including one shown at center foreground. (The Asahi Shimbun)

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