Who changed
Hamaoka’s
decommissioning records?

A nuclear plant does not become simple when its reactors stop. The machinery is cut apart over decades; materials are measured, classified, stored and eventually removed. The record of what happened is what allows a regulator, a fund manager and the next generation of workers to know what is left. At Hamaoka, that record trail now has a documented break.

Chubu Electric Power Co., Inc. acknowledged on August 27 that copies of work reports received from contractors had been rewritten in connection with fiscal 2024 dismantling at Hamaoka Nuclear Power Station Units 1 and 2. The company said altered quantities and equipment information—figures that did not match actual results—were reported to the body that manages Japan’s new decommissioning funding system.

The recipient was the 使用済燃料再処理・廃炉推進機構, abbreviated NuRO and identified on its own site in English as the Nuclear Reprocessing and Decommissioning facilitation Organization of Japan. The materials were not merely internal paperwork. They were evidence submitted in the process that led from a decommissioning performance report to a claim for payment.

What Chubu has established publicly is precise but incomplete. On May 28, 2025, it submitted rewritten copies for at least 14 work items in the fiscal 2024 plan. “At least” matters: 14 is the known floor, not a final total. The disclosure does not name the employees or units that made the changes, identify an instruction or approval chain, explain a motive, list the original and replacement figures, or state how much money was claimed or paid.

The trail went through a site check and a cost claim

The chronology published by Chubu begins at the end of April 2024, when it sent NuRO its fiscal 2024 decommissioning implementation plan. Contractors delivered their work reports at the end of March 2025. Chubu reported the year’s work results on April 11 and sent supporting evidence on May 28. It now says rewritten copies for at least 14 items were included in that package.

NuRO conducted an on-site check on July 24 and 25, 2025. Chubu filed its fiscal 2024 cost claim on September 11. The public record does not say whether the site check identified any mismatch, how broad that check was, or whether NuRO paid the claim. It would therefore be premature to describe a confirmed overpayment or fraudulent receipt. The altered evidence is established; the financial consequence is not.

The issue surfaced after the next cycle had begun. Chubu submitted evidence for its fiscal 2025 claim on June 3, 2026. Between July 3 and July 27, NuRO asked questions about dismantled material placed in storage and the volume of waste treated. On August 3, Hamaoka’s decommissioning department started checking current and past submissions. The plant confirmed the improper handling on August 17, reported it to the head of Chubu’s nuclear power division and began an internal investigation. Disclosure followed ten days later.

Why a changed copy can move money

NuRO was created in October 2016 as the Nuclear Reprocessing Organization of Japan. A 2023 revision to the governing statute expanded its duties, and in April 2024 it assumed overall management functions intended to make decommissioning across Japan more reliable and efficient.

The division of labor is deliberate. Nuclear operators remain responsible for carrying out decommissioning at their plants under Japan’s reactor regulation law. They also pay annual decommissioning contributions to NuRO. NuRO secures and manages that money, examines operators’ plans and pays claims after confirming results. The minister of economy, trade and industry approves the annual contribution framework and supervises NuRO’s operations.

In NuRO’s published process, an operator submits a plan before work begins. NuRO checks whether the proposed work is reasonable. The operator carries it out, reports the result and claims the cost. NuRO then confirms the outcome before paying from the contributions it holds. A contractor’s report is therefore part of a chain that connects physical dismantling to institutional approval and cash.

A discrepancy in dismantled quantities or equipment names can interfere with basic tests: Was the planned work performed? Does the evidence match the claimed scope? Do storage and waste-treatment figures reconcile? The disclosures do not establish that every altered entry changed the payment due. They do establish that information entering this control system did not reflect actual results.

The watchdog is reviewing itself

NuRO’s response widened the investigation beyond Chubu’s initial announcement. It directed the utility to report detailed facts for both the case and its fiscal 2025 results, determine the cause and develop prevention measures. NuRO also said it would check other operators for similar examples and ask external experts to examine the adequacy of its own procedures.

The Ministry of Economy, Trade and Industry took a parallel route. Acting under Article 70(1) of the law governing spent-fuel reprocessing and decommissioning, the minister ordered Chubu to report the facts, chronology and response; the cause and effective prevention measures; and whether similar cases exist. The deadline is September 25, 2026.

These are not duplicate exercises. NuRO is the plan reviewer and fund manager whose evidence checks are directly at issue. METI is the ministry supervising the statutory system. Their reports should make it possible to compare the company’s internal account with the body that received the documents and the ministry responsible for the framework.

A four-phase dismantling job with a 30-year horizon

Hamaoka stands on the Pacific coast in Omaezaki, Shizuoka Prefecture. Unit 1, a 540-megawatt boiling water reactor, began commercial operation in March 1976. Unit 2, an 840-megawatt BWR, followed in November 1978. Chubu decided in December 2008 to retire the two units as part of a replacement plan, and both ceased operation on January 30, 2009.

The government approved the decommissioning plan on November 18, 2009. Chubu divided the work into four phases running for about 30 years, with completion planned for the early 2040s. During Phase 1, workers prepared for dismantling, surveyed contamination and decontaminated systems. All fuel was removed from Units 1 and 2 by the end of February 2015.

Phase 2 began after approval on February 3, 2016 and focused on peripheral equipment outside the reactor area. The more consequential transition came on December 18, 2024, when the Nuclear Regulation Authority approved Phase 3. Chubu moved into that phase on December 25.

The company’s official English material describes Phase 3 work on core internals, reactor pressure vessels and containment vessels. It lengthened the phase from six years to 12 and changed the sequence so Unit 2 would precede Unit 1. Chubu has described the dismantlement of the reactor area as the first such undertaking for a commercial light-water reactor in Japan.

A separate 2026 scandal—and a shared trust problem

The altered decommissioning records must not be merged with another Hamaoka case that erupted in 2026. The present case concerns retired Units 1 and 2, reports to NuRO and a decommissioning cost claim. The other concerns seismic ground-motion work submitted in the regulatory reviews for Units 3 and 4. No official source has established that the same people, conduct or cause link the two.

Yet Chubu itself apologized on August 27 for repeated improper cases in its nuclear division. That language reflects the institutional context. In a March 31 briefing summarized by Shizuoka Prefecture, Chubu said misconduct had by then been found in at least 108 of 225 representative-wave cases in the seismic work. The company’s explanation identified inadequate detailed planning, oral instructions to contractors, insufficient checking and weak internal challenge within its nuclear civil-engineering department. An outside committee’s investigation was still continuing.

The subject matter differs, but the control point rhymes: technical or work evidence moves from a contractor and internal team into a submission relied upon by an outside institution. One submission underpins a safety review; the other supports decommissioning oversight and payment. A response limited to retraining the immediate personnel would miss the larger question of how source data, contractor instructions, approvals and external submissions are controlled across the nuclear division.

“No direct safety impact” is a boundary, not an ending

The absence of spent fuel in Units 1 and 2 materially lowers the immediate hazard. The published notices report no release of radioactive material, worker exposure or equipment malfunction. Treating this as if it were an operating-reactor accident would misstate the facts.

But dismantling records can sit at the intersection of finance, waste control and safety management. Quantities may relate to storage capacity, treatment volumes, work sequencing and the classification of dismantled material. The notices do not identify which downstream records used the altered figures. Investigators therefore need to establish the full correction boundary rather than assuming it stops at the invoice file.

Decommissioning also has an unusual memory problem. It produces no electricity revenue, lasts longer than many careers and passes through changing contractors, software and institutions. The plant that exists in 2040 will be understood partly through records made in 2024. Controls must preserve the contractor original, log every change and approver, reconcile physical inventories with claims, and give NuRO direct access to the evidence needed for independent checks.

The September 25 report will be an opening test, not a conclusion. Chubu must show the complete population of changes and any financial correction. NuRO must show what its site check and document review did—and did not—test. METI must decide whether the same weaknesses exist elsewhere in a system that is only two years old. Hamaoka’s dismantling is meant to run into the early 2040s. The credibility of its records has to last longer.