A team of Japanese scientists said Thursday that faults underneath a nuclear plant in northern Japan are most likely active, a discovery that could further delay the restart of idled reactors.
The four-member panel commissioned by the Nuclear Regulation Authority said that at least two major faults underneath the Higashidori nuclear plant in Aomori prefecture are believed to be active — a contradiction of operator Tohoku Electric Power Co's assertion that they are inactive.
The panel said the faults could cause magnitude 7-class earthquakes near the reactor, which was opened in 2005 and is among the newest of Japan's aging reactors.
"We conclude that (the operator's) claim that they are not active faults is unacceptable," said Kunihiko Shimazaki, a NRA commissioner who heads the panel. He said the scientists have presented sufficient evidence, but will hold another hearing next week to give the operator a chance to provide its view.
"If they still think they are not active faults, let's hear what they have to say. Then we'll explain our position," Shimazaki said.
Unless the operator can present evidence that reverses the current analysis, Tohoku Electric would have to re-evaluate the seismic impact and reinforce the facility before it could reopen, a process that could take years.
Tohoku Electric engineering and construction chief Akira Chigama said his company stands by its view that the faults are inactive. He said the operator's data have been accepted in past government inspections under the NRA's predecessor. That supervisory agency was disbanded after facing massive criticism of its lax supervision since the Fukushima disaster in March 2011.
The meltdowns at the Fukushima Dai-ichi nuclear plant following a massive earthquake and tsunami triggered widespread safety concerns and distrust in operator and regulators. The NRA is now setting up new safety standards that are made compulsory — a major shift from previous rules that were mostly operators' voluntary effort — and evacuation guidelines.
Only two of Japan's 50 reactors are online. The rest are suspended for checks after the Fukushima meltdowns.
Checks have been also made for seismic faults at several other plants following criticism that past investigations of faults by utilities were faulty. Although the government, desperate to stabilize Japan's energy supply and cost, has said reactors that have passed strict safety checks can resume operations, fresh investigations into faults could further delay the process.
Hiroshi Sato, a University of Tokyo seismologist, said the NRA should make a safety-first decision.
He said to ensure safety, experts should expand the investigation into faults in the northern Aomori district, home to other major nuclear facilities including a spent fuel reprocessing plant.
Although the NRA is designed to have more independence and power than its predecessors, under Japan's lax nuclear safety law, neither the regulator nor the government has legal power to order operators to shut down or take specific action with their reactors.