The Nuclear Regulation Authority has asked Kansai Electric Power Co. to re-examine the seismic resistance of its Oi plant in Fukui Prefecture on the assumption that three active faults around it might move in tandem during a quake.
The NRA made the request Friday as part of its process of checking whether reactors 3 and 4 — the only ones in Japan currently running — are safe enough to stay online after July, when new safety requirements will take effect.
At a meeting with the NRA, Kansai Electric denied that it needs to consider the potential repercussions of the three active faults being linked.
The faults are all situated within roughly 30 km of the plant, which sits on the Sea of Japan coast. Two are in Wakasa Bay to the northwest and the third is on land to the southeast.
Kansai Electric said it has found that the distance between the two seaside faults and the one on land is greater than previously estimated.
But NRA Commissioner Kunihiko Shimazaki said that an incident involving interconnected movements of the three faults is "not a bare possibility."
"I want you to hold discussions by assuming the move will occur," Shimazaki said.
If the NRA acknowledges the two reactors have no serious safety flaws, they will be allowed to operate through September, when they will be taken offline for routine maintenance and inspections.
Other power companies will have to wait for the new safety requirements to take effect in July before applying to restart their reactors.
The new rules were compiled based on lessons learned in the disaster at Tokyo Electric Power Co.'s Fukushima No. 1 power plant in March 2011.