Watchdog to rule fault line beneath nuclear plant is active

January 29, 2013

By RYUTA KOIKE/ Staff Writer

A Nuclear Regulation Authority panel of experts has endorsed a draft report declaring that a geological fault line running directly beneath a reactor building at the Tsuruga nuclear power complex is probably still active, raising questions about the plant's future and why it was built there in the first place.

"It is likely an active fault and should be taken into account during anti-seismic planning," the report says.

The panel signed off on the draft Jan. 28 and is now expected to consult other specialists before releasing it formally.

NRA Chairman Shunichi Tanaka has said that in the circumstances safety checks on the affected reactor, the plant's No. 2 unit, cannot take place--and clearing those checks is a prerequisite before idled reactors can restart.

This means Japan Atomic Power Co., the plant operator, will likely be unable to request a restart and will be compelled to decommission the reactor unless it can prove that the fault in question--known as the D-1 fault--is not active after all.

The draft report says nearby geological formations suggest the D-1 fault could have shifted at some point during the past 130,000 years, but that evidence is difficult to obtain and this conclusion is therefore more a calculated probability. However, an adjacent fault, the Urasoko fault, is known to be active, and the report says any movement there could cause the D-1 fault to move in tandem, with the same consequences for the reactor building above it.

On Jan. 28, Japan Atomic Power dismissed the draft report as "lacking scientific data." It is conducting independent surveys which aim to challenge the claim and prove that the D-1 fault is inactive. It plans to submit a survey report to the NRA in late February.

Meanwhile, on-site surveys by the NRA failed to find direct evidence relating to two fault lines running directly beneath the No. 1 reactor building at the Tsuruga plant. The agency, therefore, plans to use survey data acquired by Japan Atomic Power in assessing the status of those faults.

By RYUTA KOIKE/ Staff Writer
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The Tsuruga nuclear power plant in Fukui Prefecture (Asahi Shimbun file photo)

The Tsuruga nuclear power plant in Fukui Prefecture (Asahi Shimbun file photo)

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  • The Tsuruga nuclear power plant in Fukui Prefecture (Asahi Shimbun file photo)
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