Hamaoka Restart Reset: Data Scandal Forces Chubu Electric Back to Square One

Chubu Electric has reached the point every long-running nuclear restart project tries to avoid: not another request for data, not another round of questions, but a decision to abandon the applications that have carried Hamaoka Units 3 and 4 through more than a decade of post-Fukushima safety review.

On September 14, the utility’s board decided to withdraw the applications under Japan’s new regulatory standards because the independent investigation into its seismic-motion work left what the company called serious doubts about the reliability of the application materials and subsequent responses to regulators. Chubu says it will submit the formal withdrawal paperwork to the Nuclear Regulation Authority once preparations are complete. It also says it intends eventually to reapply.^[2]

That distinction matters. The board has made the withdrawal decision; the company’s public notice did not say the NRA had already completed the administrative withdrawal. Nor does “back to square one” mean that every engineering calculation and every piece of hardware built since 2011 must literally be discarded. It is editorial shorthand for a deeper reset: the current regulatory case can no longer be trusted as a coherent foundation, and Chubu has not yet said what can be reused, what must be recalculated or when a fresh application could be ready.

The seismic issue in plain language

The controversy centers on the selection of “representative waves” used in a fault-model approach to estimate earthquake motion. In a January 2019 NRA review meeting, Chubu said that for calculations using the statistical Green’s function method it would generate 20 ground-motion results with different conditions and select the wave closest to the average of those 20 as the representative wave.^[4]

What Chubu later disclosed was different. Under what it called Method 1, engineers created many sets of 20 motions plus a representative wave, rather than a single set, and then selected a representative wave from among those sets. Under Method 2, used from around 2018, a wave that was not initially closest to the average could be chosen first, after which the other 19 motions were selected so that the chosen wave became the one closest to the resulting 20-wave average.^[4]

By March 2026, Chubu said it had examined 225 representative-wave cases. It had confirmed Method 1 in at least 105 cases from no later than around 2012 through fiscal 2021. Interviews indicated that Method 2 had been used in roughly 80 cases around 2018–2019, although documentary confirmation at that stage covered at least three cases; another 77 cases still required additional investigation. Those were interim figures, not a substitute for the independent committee’s final case-by-case evaluation published in September.^[5]

The core regulatory problem is not captured by asking only whether a particular calculation produced a larger or smaller number. A safety review depends on the regulator being able to reproduce and challenge the method the utility says it used.

Why “reference seismic motion” sits near the heart of a restart review

Japan’s reference seismic motion—kijun jishindō, commonly referred to as Ss—is a design-basis input used in seismic safety assessment. It influences how a plant demonstrates that buildings, systems and components important to safety can withstand the earthquakes assumed for the site. Establishing it requires judgments about faults, source models, site characteristics, observed records and uncertainty.

That technical complexity is precisely why the committee resisted a one-word characterization of every act. Some questions turn on how randomness should be used and what is consistent with the objectives of the statistical Green’s function method. But complexity cuts both ways. A highly specialized process is harder for outsiders to challenge, so it demands stronger documentation, independent review and a culture in which another expert can say, “Show me exactly how you got there.”

Chubu’s own president described the reference seismic-motion work as touching the foundation of plant safety and said repeated improper conduct in that work was something that should never occur at a nuclear operator. The company’s credibility problem therefore extends beyond the numerical result of any one wave.^[3]

The investigation turned an engineering problem into a governance case

At the September 14 press conference, President Kingo Hayashi summarized findings that went well beyond technical procedure. The committee identified what the company translated in substance as a distinctive internal theory of justification: an organizational logic in which some employees came to believe that improper conduct was defensible. Chubu also acknowledged that the highly specialized nature of the work made internal monitoring and challenge structurally difficult.^[3]

Checks existed on paper. There were specialists outside the direct reporting line and an internal help-line system. But according to Chubu’s summary, those mechanisms lacked sufficient independence and objectivity and did not function effectively. Hayashi said internal warnings, including help-line reports, had been raised repeatedly without management ultimately identifying and correcting the problem.^[3]

News reporting on the committee’s findings adds detail. Jiji Press reported that a 2019 whistleblower matter reached then-President Satoru Katsuno in the form of a decision not to pursue the concern; the committee did not find that Katsuno affirmatively approved misconduct, but said more cautious judgment was warranted. Other reporting says concerns were raised internally in both 2019 and 2021 without producing an adequate correction.^[15]

Restart pressure was a factor—but that is not the same as a direct order to manipulate data

The committee also examined management pressure around the pace of the safety review. Hayashi said senior management had criticized the nuclear civil-engineering organization for delays without fully understanding that some causes were beyond the team’s control. The investigation concluded that this pressure was one factor behind the improper conduct.^[3]

The distinction is essential. The public record cited here does not establish that top executives issued a direct instruction to “make the earthquake smaller” or ordered a particular wave to be selected. The more consequential organizational finding is subtler: schedule pressure met a closed specialist culture, weak independent challenge and a pattern of internal rationalization. In that environment, people could redefine procedural deviations as acceptable steps toward a corporate objective.

The warning system failed more than once

For a nuclear operator, a strong safety culture is not demonstrated by the absence of bad news. It is demonstrated by what happens when bad news arrives. The Hamaoka case is especially damaging because questions were raised internally before the matter became public, yet the organization did not stop and resolve the issue decisively.

The failure continued after outside scrutiny began. Chubu says it had been responding to an NRA investigation into the reference seismic-motion work since May 2025. It publicly disclosed the issue on January 5, 2026. The NRA issued a formal reporting order under Article 67(1) of the Reactor Regulation Act on January 14, and received Chubu’s report on March 31.^[7][8]

In July, Economy Minister Ryosei Akazawa said he understood that improper rearrangement of data had continued even after the NRA investigation began in May 2025. He called that unacceptable in substance because it damaged trust in nuclear safety and said the ministry would respond strictly after its own reporting process.^[10]

That is a different order of problem from discovering an old spreadsheet mistake. It asks whether the organization could recognize a red flag, stop work, preserve the record and submit itself to independent challenge. In a high-consequence industry, the ability to stop is itself a safety system.

Hamaoka has already been waiting since 2011

The reset lands on a project with unusually long history. In May 2011, two months after the Fukushima Daiichi accident, Prime Minister Naoto Kan asked Chubu Electric to suspend operations at Hamaoka. Chubu’s board decided on May 9 to shut the operating Units 4 and 5 and postpone the restart of Unit 3.^[12]

Japan’s post-Fukushima regulatory system then imposed new requirements. Chubu applied for review of Unit 4 in February 2014 and Unit 3 in June 2015. Units 1 and 2 had already ended operation in 2009. Unit 3 is rated at 1,100 MW, Unit 4 at 1,137 MW and Unit 5 at 1,380 MW; the two reactors covered by the current withdrawal decision therefore represent 2.237 GW of installed capacity.^[13]

The chairman and president are leaving

Hayashi said he will resign as president on September 30. Chairman Satoru Katsuno is also stepping down. Chubu selected Senior Managing Executive Officer Minoru Yasui to become president from October 1. Hayashi said the failure could not be assigned to one department or a few employees; management and the wider organization shared responsibility.^[3]

The leadership change gives Chubu a visible break with the period in which the problem developed, but personnel changes are the easiest part of a governance repair to see. The harder evidence will be operational: whether dissenting technical views are recorded and escalated; whether internal reports are investigated independently; whether senior executives understand why a review is delayed before demanding acceleration; and whether people are rewarded for stopping questionable work rather than for making a deadline.

Chubu’s answer is an organizational rebuild

Chubu has grouped its reform direction under three themes: changing awareness and behavior, changing organizational culture, and strengthening governance and checking functions. It says the nuclear organization will be recast around nuclear safety, compliance and trust; new governance and quality-assurance functions are planned, and people from outside the nuclear division and from outside the company are to be brought into key roles.^[3][11]

The company also plans to strengthen whistleblower handling by using outside lawyers and specialist investigators where appropriate and to establish a help-line channel under the audit and supervisory structure, separate from executive management. Internal audit is to gain outside advisers. The intended message is that specialist independence cannot mean specialist isolation.

A setback inside Japan’s broader nuclear revival

The timing gives the case national significance. Japan’s Seventh Strategic Energy Plan, approved by the Cabinet in February 2025, moved policy toward maximum use of decarbonized power sources as electricity demand, energy security and decarbonization pressures rise. Government explanations explicitly include both renewable energy and nuclear power in that strategy.^[14]

But national policy cannot substitute for plant-by-plant safety review. Nuclear utilization is premised on safety, regulatory approval and public acceptance. Hamaoka is a reminder that the scarce resource in a restart program is not only megawatts. It is credibility: the regulator’s ability to trust what it is being shown, and the local community’s ability to believe that bad news will be surfaced rather than rationalized away.

Chubu itself says Hamaoka remains important for electricity demand, decarbonization and energy security and that it will not give up on reapplying. That may be a rational corporate position. But the company now has two separate cases to make. One is an engineering case that the reactors can satisfy the standards. The other is an institutional case that Chubu can be trusted to produce, challenge and disclose the evidence honestly. The second case has to be won before the first can carry full weight.

The next meaningful milestone is not a date

After a setback this large, attention naturally turns to the calendar: when will Chubu reapply, how many years will the new review take, when could a reactor finally return? Those questions matter to investors, energy planners and the region. They are also, for the moment, unknowable from the company’s official record.

More revealing milestones will come earlier. Can Chubu reconstruct the seismic evaluation with an auditable chain from assumptions to representative waves? Can an independent reviewer challenge the work without being absorbed into the same internal logic? Do help-line reports reach people with authority and independence to act? Does the board receive evidence about safety and uncertainty in a form it can actually interrogate?

Hamaoka’s restart problem is now larger than getting two reactors through a rulebook. Before Chubu can persuade Japan that a stopped plant is ready to run, it has to demonstrate that the organization itself knows when to stop. The withdrawal is not the end of that test. It is the beginning.