Japan’s Chubu Electric Power has revealed that it may have underestimated the earthquake risks at its Hamaoka nuclear plant, raising fresh safety concerns as the nation moves to revive its nuclear energy sector nearly 15 years after the Fukushima disaster.
The Hamaoka plant, located in central Japan in an area prone to a potential “megaquake,” is currently undergoing regulatory safety assessments with the goal of restarting two of its reactors. During an emergency press conference late Monday (Jan 5), Chubu Electric’s president acknowledged that the company’s previous estimate of the maximum seismic ground motion the plant could face “may have been underestimated.”
“This incident could seriously affect the (safety) review process and undermine the trust of local communities and other stakeholders in our nuclear business, and potentially shake its very foundation,” he said.
Japan largely shut down its nuclear power program following the catastrophic earthquake and tsunami in 2011, which triggered meltdowns at three reactors at the Fukushima Daiichi plant. The disaster displaced thousands of residents, caused widespread contamination, and left deep scars on the country’s energy policy.
However, Japan, which is heavily dependent on imported fossil fuels, has been seeking to restart its nuclear sector to meet growing energy demands, reduce carbon emissions, and achieve its goal of carbon neutrality by 2050. The revival of atomic energy is also seen as critical for supporting energy-intensive industries such as artificial intelligence and advanced manufacturing.
The country’s largest nuclear facility, the Kashiwazaki-Kariwa plant, is expected to resume operations later this month, pending final approval from the Nuclear Regulation Authority (NRA).
Seismic ground motion estimates are a critical component of earthquake-resistant design for nuclear plants. In September 2023, the NRA approved Chubu Electric’s estimate of 1,200 gal, a unit used to measure the intensity of ground acceleration during earthquakes.
However, in February 2025, a whistleblower alerted the NRA that Chubu Electric “may have used data different from what was presented” to the regulator, according to NRA official Keiichi Watanabe. Since then, the watchdog has been conducting its own investigation.
As a result, the NRA suspended the safety review of the Hamaoka plant in late December. Watanabe said the issue “will be discussed in meetings open to the public,” with the first scheduled for Wednesday.
Hamaoka is situated in Omaezaki, Shizuoka Prefecture, near a major seismic fault line associated with the Nankai Trough, where experts predict a massive earthquake could strike in the coming years or decades. In 2024, the Japan Meteorological Agency issued its first-ever special advisory for a potential megaquake in the region, although it was lifted a week later.
A quake in the 800-kilometer-long undersea trench, combined with a subsequent tsunami, could result in up to 298,000 fatalities and economic losses of as much as US$2 trillion, according to government estimates.
Chubu Electric said it has established a panel of lawyers to investigate the issue internally and review the company’s practices related to seismic data. The operator emphasized that ensuring the safety of residents and maintaining public trust are top priorities, even as it seeks to resume operations at Hamaoka.
The revelation comes as Japan navigates a delicate balance between energy security, climate goals, and public safety. While nuclear power is seen as a low-carbon solution, public confidence remains fragile after Fukushima, and any misstep in safety reporting risks reigniting opposition to the sector.
As the investigation continues, the Hamaoka plant’s fate remains uncertain, and the incident underscores the challenges Japan faces in safely reviving nuclear energy in a country highly vulnerable to seismic activity.
