Chubu Electric Admits Possible Underestimation of Hamaoka Seismic Risk

Chubu Electric Power Co. said on Jan. 5–6 that it may have presented data that underestimated the maximum seismic ground motion for its Hamaoka nuclear power plant, potentially affecting the Nuclear Regulation Authority’s safety examination and shaking public confidence in the company’s operations. Kingo Hayashi, president of the Nagoya‑based utility, called the matter “possible negligence” and warned it “could have a serious impact on the Nuclear Regulation Authority’s examination” and “undermine trust in our nuclear power business and shake the foundations of our operations.” Company executives publicly apologized and bowed in a gesture that reflected the gravity of the disclosure in Japan’s corporate culture.

The Hamaoka complex in Omaezaki, Shizuoka Prefecture is Chubu’s only nuclear site and sits near fault structures linked to the Nankai Trough, where seismologists expect a major Pacific earthquake in coming years or decades. The NRA had approved Chubu’s estimate of 1,200 gal for the plant in September 2023. In February 2025 a whistleblower alerted regulators that Chubu “may have used data different from what was presented” to the watchdog, NRA official Keiichi Watanabe said. Since that alert the NRA has been conducting its own probe and suspended the safety review process for Hamaoka in late December 2025.

Chubu has applied for regulatory screening to restart Units Nos. 3 and 4, screenings initiated in 2014–2015 after Japan overhauled its safety standards following the 2011 Fukushima disaster. Those reviews are now on hold, and reporting indicates the reactors are unlikely to be restarted anytime soon as regulators and the public await the outcome of the investigations. Chubu said it will establish a third‑party committee to investigate the matter internally, while the Ministry of Economy, Trade and Industry has called on the company to submit a formal report under the Electricity Business Act.

Regulatory authorities have signaled they will address the issue with public oversight. The NRA said the matter “will be discussed in meetings open to the public,” with the first such session scheduled for the Wednesday following the disclosure. A senior NRA executive described the situation as one that “completely shatters the trust in the operator” and warned it “will make people question its eligibility,” underscoring how regulatory credibility as much as technical compliance is now at stake.

Beyond immediate licensing questions, the episode reverberates across Japan’s energy policy and international perceptions of its nuclear safety culture. Japan tightened post‑Fukushima regulations to reassure domestic and global stakeholders; revelations of potential data misrepresentation test those reforms and raise legal and diplomatic risks, from investor confidence to potential scrutiny by international safety partners. The precise nature of the alleged discrepancies, including what data were used and whether calculations materially changed estimated ground motion, remains under investigation by Chubu’s planned committee and NRA probes. For now, the disclosure has reopened deep anxieties about seismic risk, corporate accountability and the path for nuclear power in a nation that must balance energy security, climate goals and public safety.