Third check for quake faults ends at Oi plant


Inspectors from the Nuclear Regulation Authority on Sunday wrapped up their third seismic survey of the Oi nuclear power plant in Fukui Prefecture.

Deputy NRA chief Kunihiko Shimazaki, who participated in the two-day survey, said the new regulator will carefully evaluate whether a crush zone known as F-6 that runs beneath the plant is an active fault.

The NRA said it might suspend the No. 3 and No. 4 reactors at the plant run by Kansai Electric Power Co. if the F-6 crush zone is determined to be an active fault. But the NRA will be hard-pressed to reach a conclusion before the two reactors undergo their regular checkups in September.

The No. 3 and No. 4 reactors at the plant in the town of Oi are the only ones in Japan be restarted since Tokyo Electric Power Co.’s Fukushima No. 1 plant in March 2011 became ground zero for the worst nuclear accident since Chernobyl.

Japan’s seismic-resistance guidelines for nuclear plants ban the construction of crucial facilities above an active fault. But a crush zone, or a fractured area of bedrock, was discovered in a test trench Kansai Electric dug to the south of the No. 3 unit. But the utility claimed the crush zone could be classified as an F-6 rather than an active fault.

Shimazaki said the NRA will focus on the relationship between the crush zone found in the new test trench and an F-6 crush zone that was discovered in a separate test trench that was opened before Kepco applied for an NRA screening of the No. 3 and No. 4 reactors under new safety standards introduced in early July. The old test trench has already been closed.

The screening is a prerequisite for restarting the reactors after the mandatory inspection.

The NRA inspection group consists of Shimazaki and four outside experts. Two of them were absent during the latest survey.

Shimazaki said he would like to reach a unanimous conclusion on whether an active fault lies under the Oi plant. But even with that, it would still take a lengthy time to draw up the evaluation report, he said.