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Another active fault (Higashidori plant)

Faults under Aomori nuclear plant site probably active: NRA panel





A panel under the Nuclear Regulation Authority agreed Thursday that faults under Tohoku Electric Power Co.'s Higashidori atomic plant in Aomori Prefecture are probably active, rejecting earlier arguments to the contrary by the utility.

The situation does not violate the nation's nuclear plant laws because the faults do not run directly beneath the sole reactor at the Higashidori complex, but it may make it difficult for the utility to have the reactor restarted anytime soon.

The Higashidori plant is the third site where the NRA, which debuted in September, has sent experts to check faults suspected of being active.

The focus of the discussion has been the fault F-3, which runs vertically through the plant's premises, and fault F-9, which parallels F-3.

Tohoku Electric has said deformations observed in geological layers were created by clay minerals that swelled on exposure to water, and not because active faults exist under the complex.

The reactor at the Higashidori plant started commercial operations in December 2005 and went offline for regular checks in February 2011, shortly before the nuclear crisis erupted at Tokyo Electric Power Co.'s Fukushima No. 1 plant.

The area just north of the Higashidori plant is also where Tepco plans to build its own Higashidori plant.

Another team of experts led by the regulatory body has already agreed that a fault running directly underneath a reactor at Japan Atomic Power Co.'s Tsuruga plant in Fukui Prefecture is probably active, an assessment that could leave the utility with no option but to scrap the unit.

A similar team appointed by the NRA visited Kansai Electric Power Co.'s Oi plant, also in Fukui Prefecture, for an assessment, but it has not yet reached a conclusion. Two reactors at Kepco's Oi plant are the only units now operating in Japan.




Higashidori N-plant crush zones seen active

A Nuclear Regulation Authority research team on Thursday agreed that crush zones beneath the Higashidori nuclear power plant in Aomori Prefecture are likely to be active faults.

"It is hard to accept any claim that the crush zones are not active faults," said NRA Acting Chairman Kunihiko Shimazaki, who heads the team of experts named by the regulatory body.

The team will meet again Wednesday to hear explanations from Tohoku Electric Power Co., the operator of the nuclear power plant. If the nuclear authority concludes the crush zones, or fractured areas in bedrock, are really active faults, it would be difficult to restart the plant's 1.1-million-kilowatt reactor, at least for the time being.

The team has confirmed the likely presence of an active fault under Japan Atomic Power Co.'s Tsuruga nuclear power plant in Fukui Prefecture. Higashidori is the second facility beneath which the team has discovered the problem.

Adjacent to the Higashidori plant, a Tokyo Electric Power Co. nuclear plant is under construction. TEPCO's plant will also face a similar problem, as some of the crush zones extend under the site of TEPCO's facility.

It is extremely difficult to rule out the possibility that the zones under TEPCO's site are active faults, said team member Yasuo Awata, researcher at the National Institute of Advanced Industrial Science and Technology.

The team focused mainly on the F-3 and F-9 crush zones, both of which run north-south. The zones are only 200 to 400 meters from the No. 1 reactor building of Tohoku Electric's Higashidori plant.

Team member Heitaro Kaneda, associate professor at Chiba University, warned that if these zones move, an earthquake with a magnitude of more than 7 could occur.

Tohoku Electric has not assessed the effects of possible crush zone movements on the reactor or any other facilities in the Higashidori plant. The firm may have overlooked the possibility the crush zones will move, Shimazaki told a news conference.

(Dec. 22, 2012)

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