By KEITARO FUKUCHI/ Staff Writer
January 10, 2024 at 18:55 JST
The Shika nuclear power plant in Ishikawa Prefecture on Jan. 2 (Tatsuya Shimada)
The shaking of the idled Shika nuclear power plant in Ishikawa Prefecture during the New Year's Day earthquake slightly exceeded the estimated maximum levels, the Secretariat of the Nuclear Regulation Authority announced on Jan. 10.
However, the secretariat of the nuclear watchdog said the necessary power supply for cooling the spent fuel is secure and there are no safety issues with the plant.
The secretariat released the report from Hokuriku Electric Power Co., the plant operator, at a regular meeting of the NRA.
The safety estimates were made by the NRA's predecessor, the Nuclear and Industrial Safety Agency, which was abolished in 2012.
The No. 1 and No. 2 reactors at the Shika nuclear plant were taken offline long before the earthquake. The No. 2 reactor is currently under review for new regulatory standards before it can be restarted, while the operator has not yet applied for the review for the No. 1 reactor.
Different parts of a nuclear power plant respond differently to seismic activity. Each facility and equipment has a particular period where it’s most vulnerable to shaking.
For these specific periods, operators estimate the acceleration of the maximum intensity of possible shaking, using a unit of measurement called gals.
In the Noto Peninsula earthquake on Jan. 1, the shaking slightly exceeded the estimated levels in some period bands. But important facilities such as reactor buildings and pressure vessels were not in the susceptible periods, the secretariat said.
At the idle Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture, which is operated by Tokyo Electric Power Co., the shaking was below the estimates for all period bands.
At the meeting, the secretariat also showed the status of monitoring posts measuring radiation levels around the Shika nuclear plant.
According to the authority, after the Jan. 1 earthquake, which recorded a maximum intensity of 7 on the Japanese seismic scale, monitoring posts were unable to take measurements at 18 locations, mainly 15 kilometers or more north of the Shika plant.
Based on the results of the on-site checks and the later restoration of communications, the cause of the missing measurements is believed to be a communication malfunction.
The number of missing measurements has gradually decreased since the quake.
As of 10:50 a.m. on Jan. 10, the figure declined to seven locations. Five of these have been replaced with alternative monitoring posts.
The NRA’s guidelines state that monitoring posts are used to decide whether evacuation is necessary in the event of a nuclear accident.
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