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Oi fault - Not enough data?


November 8, 2012

Experts to gather more data before conclusion on faults under Oi plant



TOKYO (Kyodo) -- A team of experts investigating the Oi nuclear power station in western Japan decided Wednesday to carry out further field surveys and collect more data to determine whether active faults are running under the country's only operating atomic power plant.

"It's desirable for the five members to reach a conclusion by consensus," Kunihiko Shimazaki, a commissioner of Japan's nuclear regulatory body and head of the investigation team, said at a meeting of the team, attributing the failure to reach a conclusion to a lack of sufficient data.

If the experts conclude there is an active fault that could undermine the safety of the plant, the Nuclear Regulation Authority is expected to ask plant operator Kansai Electric Power Co. to suspend the two operating reactors at the Oi plant in Fukui Prefecture.

The focus of the discussions has been on displacements found at trench walls in the northern part of the plant's premises during an on-site investigation last Friday, with team members divided over whether to view them as resulting from active faults or a landslide.

Toyo University professor Mitsuhisa Watanabe has said the displacements can be considered active faults and that they may be an extension of a fault called F-6, a zone of crushed rocks which runs north-south between the plant's Nos. 1-2 reactors and Nos. 3-4 reactors.

Watanabe was chosen as the member of the team because he pointed out in June that the F-6 could move together with active faults outside the plant and damage a water channel that would be used to take in seawater to cool reactors in the event of an emergency.

He expressed concern during the meeting that Shimazaki's decision to continue further study may make the investigation process drag on. "I thought this panel's mission is to decide, with a sense of speed, whether there is no danger in terms of active faults, given that the Oi plant is actually operating," he said.

But Shimazaki insisted the members would be able to reach a consensus as long as there is "proper data."

To gather more data, the seismologist said there is a need to dig deeper into the trench in question and excavate a new trench closer to a point where the F-6 is said to have been confirmed when the utility sought to build the Nos. 3 and 4 reactors.

"If this (F-6) fault shows up, it will become very clear on how it would affect which part of the plant," Shimazaki said.

But the investigation may take time, with the length of the new trench expected to reach up to 300 meters.

The next meeting of the team will be convened when one or more members find an important "observed fact" as a result of the additional research, Shimazaki said.

During the meeting, Kansai Electric officials reported to the experts they have not confirmed in the F-6 fault features that are usually seen in active faults.

The Nos. 3 and 4 reactors resumed operation in July after all of the country's reactors went offline amid strong public concern over the safety of nuclear power in the wake of Tokyo Electric Power Co's Fukushima Daiichi plant disaster last year.

The two reactors have remained online since, with the Nuclear Regulation Authority's predecessor saying the fault is unlikely to be active. The body was launched in September as part of the country's efforts to enhance nuclear regulations.

In quake-prone Japan, utilities are not allowed to build reactors and other facilities important for the safe operation of reactors directly above active faults.

NRA to continue Oi fault probe




Staff writer

A panel of experts under the Nuclear Regulation Authority decided Wednesday to continue examining a fault running under the Oi nuclear plant in Fukui Prefecture, rejecting calls by one of its members that the facility immediately cease operations.


It was the panel's second meeting since its members conducted an on-site geological survey Nov. 2 at the Oi complex, the only nuclear plant to be reactivated following the Fukushima disaster last year. As part of the survey, they examined the F-6 crushing belt fault that runs directly below critical pipes carrying coolant water for reactors 3 and 4 during emergencies.

The two units were restarted in July amid a public outcry.

If the fault is considered active, the NRA is likely to demand that all operations at the Oi plant immediately halt. However, the panel failed to reach a conclusion Wednesday.

At its meeting, Kansai Electric Power Co., which operates the Oi facility, issued a new 66-page interim report concluding that geological traces and analysis suggest the fault is not active and has not moved recently.

But Toyo University professor and panel member Mitsuhisa Watanabe argued the geological samplings are insufficient to support Kepco's interim conclusion.

Watanabe, who believes the fault is active and potentially highly dangerous, demanded the panel curtail its technical discussions, but its deputy chairman, Kunihiko Shimazaki, declared it would hold further sessions, saying, "I don't think we have reached any conclusion for now."

Meanwhile, panel member Daisuke Hirouchi, an associate professor at Shinshu University, said he would prefer to conduct another on-site survey before arriving at a definitive conclusion.

The panel's ultimate decision is likely to massively influence Japan's atomic and basic energy policies, since strong antinuclear sentiment among the public has prevented the government from firing up any more reactors since the Oi units, and because crippling supply shortages are feared in the Kansai region if those two reactors were to be shut down.

Kepco claims it won't be able to meet projected peak power demand if the Oi reactors are idled.

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