Will Ohi fault study impact all offline reactors?

The Ohi nuclear power plant, the only nuclear plant currently operating in Japan, sits on what may be a seismic fault in the earth’s crust, a geologist has warned, saying it is “very silly” to allow it to continue operating.

According to Toyo University professor Mitsuhisa Watanabe, nuclear regulators and power companies have a long history of willfully underestimating the danger posed by active faults near a number of reactors, out of fear their reactors could be shut down.  “We have to sound the alarm as soon as we find the possibility of active faults,” he said. “The accident in Fukushima had really never been imagined. Scientists must learn from that.”

Watanabe, a tectonic geomorphologist, is part of a five-member team tasked by the Nuclear Regulation Authority with looking into the tectonic situation underneath the plant, which houses the country’s only working reactors.  All of the other members on the Nuclear Regulation Authority’s expert panel have admitted that the fault, named F-6, could be active and pose a serious danger.

Watanabe believes this is good enough reason for the government to order a temporary shutdown and conduct exhaustive geological surveys.  To ensure independence, the panels should be given a budget and the authority to conduct on-site surveys wherever they believe it’s necessary, he said.  “We should not repeat the same mistake that was made in Fukushima,” he said.

“If you can’t deny the possibility that it may be an active fault, we should not ignore the risk. The plant should first be suspended.”  Watanabe said a one-time survey like that will be far from sufficient to examine all of the suspected faults within the compound.

 

“The nuclear regulator and power companies have long tried to underestimate (the danger) of active faults, worrying it would affect power supply capacity,” Watanabe said, using the Shimane nuclear plant in Matsue, Shimane Prefecture, as an example.

Takashi Nakata, now a professor emeritus at Hiroshima University, had long pointed out there is a fault near the Shimane plant that was overlooked by Chugoku Electric Power Co. before it built the facility.

Initially the utility denied the existence of the active fault. Then when it admitted in 1998 the fault was there, it estimated the length at only 8 km.

Facing further criticism from Nakata, Watanabe and other experts, Chugoku Electric extended the estimated length of the Shinji Fault to 10 km in 2004 when it applied for approval to build a third reactor at the plant.

The company eventually was forced to revise its estimate to 22 km in 2008, but only after outside experts dug up the ground to show the fault actually extend that far.

The longer a fault is, the more powerful the earthquake it can cause, which is possibly why Chugoku Electric was reluctant to admit the Shinji Fault stretches as far as it does, Watanabe said.

Source: The Japan Times

 

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