Japan’s Nuclear Regulation Authority (NRA) has accused Chubu Electric Power Co of manipulating data following a regulatory investigation into its fraudulent earthquake risk data relating to the Hamaoka NPP in Shizuoka Prefecture. “We suspect there was a cover-up,” NRA Chairman Shinsuke Yamanaka told a news conference. “I feel there was malicious intent,” he said.
NRA has instructed its secretariat to investigate whether Chubu Electric executives were involved and will decide its formal response to the scandal after confirming the details. Chubu Electric said in a statement: “We take it extremely seriously and apologize again from the bottom of our hearts.”
Chubu Electric used a method different from what was reported to the NRA to estimate a maximum seismic ground motion that the plant could experience, during safety screenings crucial for the restart of the plant’s unit 3&4 reactors.
The company allegedly underestimated the maximum seismic ground motion by selecting favourable data while suggesting that the figures came from proper calculation. Such irregularities are believed to have been carried out across multiple departments.
The NRA secretariat said Chubu Electric retroactively collected and rewrote data linked to the cherry-picking after it began hearings over the scandal in May 2025, affecting 69 of the 225 sets of data being investigated.
Chubu told NRA that it had randomly collected 20 seismic wave data points and selected data close to the average for the NRA screening, when it had actually asked a contractor to select data favourable to the company from more than 1,000 data points. In some cases, the cherry-picking involved nearly 30,000 data points.
The company applied for NRA screenings for units 3&4 between 2014 and 2015. In 2023, NRA broadly approved the company’s assumption for the maximum seismic ground motion. However, NRA became aware of the data fraud through an external tipoff in February 2025. Chubu Electric made public the misconduct in January, setting up a third-party committee to investigate the matter.
The Hamaoka Nuclear Power Plant sits directly above a major subduction zone near the intersection of two tectonic plates, making it highly vulnerable earthquakes. The plant consists of five boiling water reactors (BWRs). Units 1&2 were permanently retired in 2009 and dismantling of unit 2 began in 2025. Units 3-5 were shut down after the 2011 earthquake and tsunami. Chubu Electric subsequently built a massive 22-metre-high sea wall to protect against tsunamis and applied for safety screenings to restart units 3&4.
