NRA says no need to review quake hazard for Oi

July 13, 2016

Nuclear authority says Oi plant's quake hazard not underestimated

http://mainichi.jp/english/articles/20160713/p2g/00m/0dm/068000c

TOKYO (Kyodo) -- Japan's Nuclear Regulation Authority decided Wednesday there is no need to review an estimate of the biggest potential earthquake around the Oi nuclear power plant on the Sea of Japan coast after a recalculation prompted by a former member warned it may be understated.

Seismologist Kunihiko Shimazaki, who was one of the five commissioners of the authority, warned last month that the NRA may have underestimated quake hazards at some nuclear plants by using a faulty formula in calculating the seismic ground motions which nuclear reactors are required to withstand.

After the authority recalculated the seismic motions using another formula, it found the maximum scale of the earthquake around the Kansai Electric Power Co. plant in Fukui Prefecture was still smaller than the figures already approved in the safety screening.

"It was good that we calculated it afresh," said Akira Ishiwatari, who succeeded Shimazaki at the authority, noting the results fell within the standards as the original estimate was calculated to be on the safe side.

Shimazaki has said he studied the initial calculating formula after he left the commissioner's post in September 2014 and confirmed it would underestimate the scale of earthquakes when applied to faults almost perpendicular to the land surface.

Japan has imposed tougher nuclear safety standards since the meltdowns at the Fukushima Daiichi nuclear power plant triggered by the huge earthquake and tsunami that hit northeastern Japan in March 2011.