A geological fault line that runs directly beneath a reactor building at the Shika nuclear plant in Ishikawa Prefecture is likely an active one, a government agency has warned, despite the plant operator's repeated assertion over 25 years that it is inactive.
The government's safety standards mandate that key nuclear power facilities not be built directly over an active fault. If the fault is identified as active, that could force the site to be declared inoperable and the Shika nuclear plant, which is currently offline, to be decommissioned.
"I will make a decision after hearing the expert opinions," industry minister Yukio Edano told a news conference on July 17. "I will react promptly if it is learned anew that (the fault in question) is an active fault."
This is the second time the Nuclear and Industrial Safety Agency (NISA) has pointed out that an active fault may lie directly beneath a nuclear reactor building, following a similar warning in April concerning Japan Atomic Power Co.'s Tsuruga nuclear plant in Fukui Prefecture.
NISA was expected to hear expert opinions during a hearing on the afternoon of July 17 and order Hokuriku Electric Power Co., the Shika plant operator, to conduct drilling surveys if the need arises.
The fault in question, about 300 meters long, runs directly beneath the Shika plant's No. 1 reactor building. When Hokuriku Electric applied for a permit to build the No. 1 reactor in 1987, it maintained that the fault was a product of erosion and was not active. Screenings by NISA also ruled out the possibility of being an active fault.
Hokuriku Electric also denied it was an active fault when it applied for a permit to build the No. 2 reactor in 1997 and when it reviewed the plant's safety following the 2006 amendment of the government's anti-seismic guidelines.
"We confirmed the presence of eight fault lines when we built the power plant," said a Hokuriku Electric representative. "Safety reviews based on the revised anti-seismic guidelines endorsed that the faults are not active. There is no change in our view that there is no active fault."
But Mitsuhisa Watanabe, a professor of tectonic geomorphology at Toyo University, disagrees.
"As far as I can tell from the survey maps, I think (the fault in question) is an active fault," Watanabe said. "It may even have moved twice. I am very skeptical about the quality of previous government screenings."
Following the Great East Japan Earthquake last year, which triggered a disaster at the Fukushima No. 1 nuclear power plant, NISA has been reviewing geological fault lines lying near nuclear power plants across Japan.
Re-examination of materials submitted by Hokuriku Electric indicated that the fissure in question was likely an active fault that has shifted in relatively recent times, or during the past 120,000-130,000 years. Experts therefore recommended conducting a reassessment.
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