NRA team starts second fault survey at Oi plant


A Nuclear Regulation Authority team started a second survey Friday at the Oi nuclear power plant to determine whether there are active faults beneath it.

If the team confirms the presence of an active fault in the two-day study, Kansai Electric Power Co. will have to stop reactors 3 and 4, currently the only active reactors in Japan.

The previous on-site survey was conducted in November.

The team is investigating a crush zone, or a fractured area in bedrock, that is believed to run underneath a seawater intake channel for the emergency cooling system for reactors 3 and 4.

After the first study, the team was unable to rule out that the crush zone known as F-6 is an active fault. But the team did not reach a final conclusion because it could also not exclude the possibility that F-6 was caused by landslides.

The second survey includes inspections of pits newly dug by Kansai Electric, which is engaged in drilling work under an order from NRA deputy chief Kunihiko Shimazaki, who heads the team.

Kepco has dug deeper and wider pits in a northern corner of the plant’s premises to see whether F-6 reaches the area. More drilling requested by the authority has not finished, but Shimazaki said the team may be able to reach a conclusion without waiting for that to happen.

At a conference held prior to the second survey, Shimazaki noted that Kepco people have complained that at least some of the research appears unnecessary. “But we do not see anything wasteful,” Shimazaki stressed.

F-6 is believed to run north to south between units 2 and 3. If F-6 is active and moves, the emergency seawater intake channel for units 3 and 4 may be affected.

The channel is a crucial facility that would be used if the reactors lose normal cooling functions. Japan bans construction of nuclear plants on active faults.