Last week's powerful earthquake in central Japan inflicted stress on parts of a local nuclear power plant that exceeded the limit anticipated in the facility's design, according to a report shared in a safety panel meeting on Wednesday.
The report, discussed at a regular session of the Nuclear Regulation Authority, indicated the potentially alarming readings of ground acceleration did not appear to pose an immediate safety threat to the facility in Shika on the Noto Peninsula.
The magnitude-7.6 quake hit the power plant as the authority, a government affiliate, was screening proposed safety measures toward reactivating one of its two reactors operated by Hokuriku Electric Power Co. Both were offline when the quake occurred on New Year's Day.
The quake registered a maximum 7 on the country's seismic intensity scale in Shika, Ishikawa Prefecture, on the Sea of Japan coast, according to the weather agency.
During Wednesday's meeting, Akira Ishiwatari, a geologist who handles earthquake-related issues on the panel, said, "As the latest quake has caused enormous impacts, we need to draw on the results of research by experts" in future screening of safety measures.
Shinsuke Yamanaka, chief of the authority, told reporters that such seismic research by experts may take years, and that the activity in undersea faults which triggered the latest quake "must be factored in as new knowledge" in updating safety standards.
Yamanaka, an expert on nuclear power engineering, also urged the operator to get to the bottom of a breakdown of electric transformers installed at its Nos. 1 and 2 reactors that has partially prevented the Shika plant from receiving power supplied from outside.
Hokuriku Electric has said the plant can keep cooling used fuels after the latest quake.
Nobuhiko Ban, another panel member and expert on protection from radiation exposure, called it "a huge problem" that real-time radiation levels have not been monitored at some locations near the Shika plant after the quake, and proposed using aircraft and drones for the purpose.
The operators of nuclear plants in Japan have kept many reactors shut down in recent years while improving power procurement systems in the event of an emergency, after the Fukushima Daiichi complex suffered reactor meltdowns due to a complete blackout following the March 2011 quake and tsunami.
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