Hamaoka Nuclear Plant Restart Likely Delayed by Improper Earthquake Data

The Yomiuri Shimbun

13:53 JST, January 6, 2026

The Hamaoka nuclear power plant in Omaezaki, Shizuoka Prefecture, is highly likely to face a major setback in its restart timeline, as the reporting of improper seismic data has undermined the safety screening process.

The Hamaoka nuclear power plant became the subject of concern on Monday, when it was revealed that Chubu Electric Power Co. had reported data to the Nuclear Regulation Authority that potentially underestimated the scale of expected earthquake tremors.

With the very foundation of the screening now overturned, a further delay in the restart appears unavoidable. Local municipalities near the plant have also criticized the situation.

At a press conference held Monday afternoon at Chubu Electric’s headquarters in Nagoya, company representatives faced a barrage of questions, including whether the company would withdraw its application for review and if it still intended to pursue a restart.

President Kingo Hayashi stopped short of giving specifics, stating: “We are in no position to comment on the resumption of the screening or the timeline. Our only option is to proceed while fundamentally restructuring our nuclear division.”

For Chubu Electric, this revelation follows its November announcement regarding misconduct in the administrative procedures for safety-related construction at the Hamaoka nuclear power plant.

In addressing the series of recurring problems, Hayashi noted, “If necessary, we must examine the relationship between our nuclear division and executive management, as well as the state of our overall corporate governance.”

The Hamaoka plant is located within the projected focal zone of a Nankai Trough earthquake. Following the 2011 Great East Japan Earthquake, the Hamaoka plant’s Nos. 3, 4 and 5 reactors were shut down. Its Nos 1 and 2 reactors were already slated for decommissioning.

With the goal of restarting the three units, Chubu Electric filed applications for safety reviews with the NRA for the No. 4 reactor in February 2014 and the No. 3 reactor in June 2015.

The NRA gave broad approval to the design basis ground motion — the maximum expected tremor that serves as the benchmark for earthquake-resistant design — in September 2023, followed by approval of the design basis tsunami, representing the maximum expected tsunami, in October 2024.

Chubu Electric had aimed to finalize both the plant facility screenings — covering reactor buildings and equipment — and the investigations of on-site geological faults by this spring.

“Because data regarding design basis ground motion requires highly specialized expertise, it may have become a breeding ground for misconduct due to a lack of internal oversight within the utility company,” said Prof. Hiroshi Yamagata of the Nagaoka University of Technology, who specializes in safety engineering. “Unless they change their organizational culture, establish a checking system and resubmit technically correct data, the review will likely not be able to proceed.”

In Shizuoka Prefecture, home to the Hamaoka nuclear power plant, a wave of shock and resentment spread, especially as expectations for an early restart had been on the rise.

“This is a serious matter that undermines the trust of the prefectural citizens in Chubu Electric and the nuclear power business, which is extremely regrettable. We will call on the central government for strict screening, guidance and supervision,” said Shizuoka Gov. Yasutomo Suzuki.

Mayor Masaru Shimomura of Omaezaki, where the plant is located, released a comment stating, “I recognize this as a serious issue that could have a major impact on safety evaluations.”

Mayor Takashi Kubota of neighboring Kakegawa demanded that the company conduct a thorough investigation and explain the results to the city and the local community.