” Japan needs to review its current method for screening nuclear plant safety, seismologist and former senior regulator Kunihiko Shimazaki said in a recent interview.
The current method risks underestimating the magnitude of possible earthquakes that may hit nuclear plants, Shimazaki, former acting chairman of the Nuclear Regulation Authority, said.
He said a review was needed on the method to calculate the design basis earthquake, or the maximum quake motion that can occur around a nuclear plant, which is currently part of the NRA’s screening procedures.
Shimazaki said that he confirmed the need for such a review after examining data on powerful quakes that hit Kumamoto Prefecture and other areas in Kyushu in April.
“The NRA has to be aware that the current screening procedures have shortcomings,” he said, adding it is “very dangerous to keep using the method.”
Before leaving the NRA in September 2014, Shimazaki was in charge of assessing quake and tsunami impacts as part of its nuclear safety screening process.
The current method risks underestimating design basis earthquakes when it is applied to vertical faults found mainly in western Japan, he said.
The design basis earthquakes for Kansai Electric Power Co.’s Takahama and Oi nuclear plants, both in Fukui Prefecture, and Kyushu Electric Power Co.’s Genkai nuclear plant in Saga Prefecture, should be recalculated based on a different method, he said.
The NRA should draw up a revised method by taking into account new data, including on strong tremors such as the Kumamoto quakes, Shimazaki said.
The No. 3 and No. 4 reactors at the Takahama plant have passed the NRA’s safety screening. The NRA is expected to approve Kansai Electric’s request for extending operational periods at the plant’s No. 1 and No. 2 reactors beyond 40 years, a basic lifetime for nuclear reactors in Japan. ”