Chubu Electric Power Co. continued to commit earthquake risk data fraud involving its Hamaoka nuclear power plant in central Japan even after regulators opened an investigation into the practice, the secretariat of the Nuclear Regulation Authority said Wednesday.
The secretariat unveiled the findings when it reported the outcome of its on-site inspection of the nuclear plant in Shizuoka Prefecture over the scandal.
The power supplier used a method different from that reported to the NRA to estimate the maximum seismic ground motion that the plant could experience during NRA safety screenings crucial for the restart of the plant¡¯s No. 3 and No. 4 reactors.
The company allegedly underestimated the maximum seismic ground motion by selecting favorable data while pretending that the figures were determined using the proper calculation.
Chubu Electric continued to commit the data fraud even after the secretariat started hearings over the issue in May last year, affecting 69 of the 225 sets of data being investigated, according to the NRA secretariat.
The company applied for NRA screenings of the No. 3 and No. 4 reactors between 2014 and 2015. In 2023, the NRA broadly approved the company¡¯s assumption of the maximum seismic ground motion.
The NRA became aware of the data fraud through an external tip in February 2025. Chubu Electric made the misconduct public in January this year, setting up a third-party committee to investigate the matter.
NRA Chairman Shinsuke Yamanaka has signaled the possibility of withdrawing its approval for the reactors because of the misconduct. The NRA will make a final decision after reviewing a report from the third-party committee.
The on-site inspection by the NRA secretariat has also found that almost no records had been kept from when the maximum seismic ground motion was established.
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