NRA chairman says faults under Higashidori likely active –Rokkasho may also be investigated

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Kunihiko Shimazaki, acting chairman of the Nuclear Regulation Authority, said Thursday that the movements underground faults underneath Tohoku Electric Power Co.’s Higashidori nuclear plant are likely to have been associated with an active fault

He made the remark at a press conference after conducting an on-site survey of the plant in the northeastern prefecture of Aomori with other experts. The experts confirmed four crush zones including those running near the No. 1 reactor building.

At a hearing held before the Great East Japan Earthquake last March by the now-defunct Nuclear and Industrial Safety Agency, experts pointed out that these crush zones might be active faults.

On Friday, the experts from the newly-formed NRA will continue the survey to learn when those zones moved and find out whether there is any possibility of the zones moving again.  Next Thursday, the experts will hold an evaluation meeting to discuss their findings.

Tohoku Electric, which supplies power to the Tohoku region including Aomori, has stated flatly, “there is no active fault nearby,” and explained that fault slips under the plant site are caused by changes in groundwater levels, and that the strata inflates after sucking in water.

But Shimazaki said he cannot give the nod to the explanation.

Survey team member Yota Kumaki, a professor at Senshu University, said that the claim by Tohoku Electric raises many questions.  If the faults are judged to be active, however, there must be a main active fault nearby, the only question is where is it located?  Many experts believe it could be located on the peripheral fault on the continental shelf, running along the seabed about 7 kilometers east of the Higashidori plant.  Tohoku Electric has said the fault, which runs north and south for more than 80 kilometers, is not active.

The highlights of the field survey are expected to be two faults, the “F-9” and “F-3” faults which run parallel in a north-south direction.  The crush zones running below the power plant are considered by some experts as being at risk of moving in tandem with a main active fault.

“F-3” that extends to approximately 200 meters of the reactor building have been identified in a survey of Tohoku Electric Power as well, “F-9” and had been Tsuranui the site.

Yasuo Awata, chief scientist for the National Institute of Advanced Industrial Science and Technology doubted the utilities explanation for the displacement, saying that the “description of the Tohoku Electric Power does not make sense.”

Japan Nuclear Fuel Ltd.’s Rokkasho reprocessing plant and the Electric Power Development Co.’s Oma nuclear power plant, currently under construction, are near the peripheral fault. It is likely experts will discuss the quake-resistance of these two plants.

Source: JiJi Press

Source: NHK

Source: The Daily Yomiuri

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