Trust in Japan's nuclear watchdog, the Nuclear Regulation Authority (NRA), has been jolted. At hand is an issue raised by Kunihiko Shimazaki, former acting chairman of the NRA. Shimazaki pointed out that Kansai Electric Power Co. underestimated the maximum shaking that could occur during an earthquake at its Oi Nuclear Power Plant in Fukui Prefecture.
Shimazaki is an authority on seismology, having formerly served as president of the Seismological Society of Japan. While serving in the NRA, he handled screening of power companies' earthquake predictions for nuclear power plants including the Oi nuclear plant.
After he stepped down two years ago, he re-examined data and found the method of calculating standard ground motion (the maximum shaking that would occur during an earthquake) was inappropriate in some cases, depending on the type of fault. This could lead power companies to underestimate figures, he apparently found in his research.
If Shimazaki's argument is correct, the Oi Nuclear Power Plant could come under pressure to provide even greater reinforcement against quakes.
The NRA had for the most part accepted Kansai Electric's data, but following the claim by Shimazaki, a new calculation on ground motion was performed using a method differing from that adopted by the power company. As the figure was below that presented by Kansai Electric, it determined that the utility had not underestimated the shaking, and during a regular meeting on July 13, it decided against revising Kansai Electric's figure.
Shimazaki, however, objected, saying that the recalculated figure should have greatly surpassed the original figure for standard ground motion. The reason is that during screening, the outcome of calculations is normally multiplied by 1.5 to provide an added element of safety, but this wasn't done.
The new calculation was performed by the secretariat of the NRA. A member of the secretariat who talked with Shimazaki admitted that the renewed calculation was repeatedly stretched, and had "no accuracy." The member added, "It's not known how much leeway should be given." It couldn't be helped if the secretariat were accused of adopting its approach to avoid criticism that the estimate for envisaged damage was too low. The fact that the NRA accepted without questions its secretariat's explanation that Kansai Electric's estimate was sufficient raises doubts about its competence.
There are no experts on seismology among the NRA's five commissioners. NRA Chairman Shunichi Tanaka has expressed the opinion that the calculated figure for standard ground motion at the Oi Nuclear Power Plant doesn't have to be reviewed. We worry whether quake resistance has been calculated properly.
Shimazaki has suggested to the NRA that it listen to a wide range of opinions from experts in seismology and incorporate the good ones into its screening. Even if experts differ in their evaluations of Shimazaki's research results, his suggestion to the NRA itself is appropriate.
Tanaka, however, commented, "We don't have the leeway to do that and it's not our job to do it either." We can only be skeptical about such a stance.
The NRA is supposed to be the final fortress in ensuring nuclear safety. We hope that it will try to make improvements to methods of calculating quake resistance of its own accord.