During the ongoing dismantling of the Fugen Advanced Thermal Reactor in Fukui Prefecture, workers encountered unexpected leaks of water contaminated with tritium, a radioactive isotope of hydrogen. The incident, reported by Japanese media and confirmed by the plant’s operator, has reignited concerns over the safety protocols governing the decommissioning of aging nuclear facilities. While no immediate health threat to nearby residents has been identified, the leak underscores the technical challenges of handling legacy reactors that were built before modern safety standards were established. This article examines the circumstances of the leak, the regulatory response, the technical hurdles of reactor demolition, and the broader implications for Japan’s nuclear decommissioning program.
Leak discovered during demolition
On December 22, 2025, workers cutting a concrete slab at the Fugen site noticed a faint, discolored seepage from a buried pipe. Subsequent testing revealed tritium concentrations of 1,200 becquerels per litre (Bq/L), well above the Japanese environmental limit of 150 Bq/L for drinking water. The water was quickly contained, and the area was cordoned off while specialists from the Nuclear Regulation Authority (NRA) arrived to assess the situation.
Technical challenges of decommissioning Fugen
Fugen, commissioned in 1979, was Japan’s only advanced thermal (heavy‑water) reactor. Its design features extensive underground piping and shielding structures that were never intended to be dismantled. Over the decades, corrosion, sediment buildup, and limited documentation have turned the demolition into a complex engineering puzzle. Key challenges include:
- Identifying hidden water pathways that may harbor radioactive contaminants.
- Ensuring that cutting and removal activities do not breach containment barriers.
- Managing large volumes of contaminated water with limited on‑site treatment capacity.
Regulatory response and mitigation measures
The NRA has ordered an immediate suspension of all cutting operations within a 200‑metre radius of the leak site. A task force comprising the operator, local authorities, and independent radiation experts is now overseeing a multi‑step remediation plan:
- Extraction of the contaminated water using portable filtration units certified for tritium removal.
- Verification of water quality through continuous monitoring stations installed around the plant.
- Re‑evaluation of the demolition schedule to incorporate additional safety checkpoints.
Officials emphasize that the measured tritium levels, while above the legal limit, pose no acute radiation risk to the public, as tritium emits low‑energy beta particles that are largely harmless unless ingested in large quantities.
Broader implications for Japan’s nuclear future
The Fugen incident arrives at a critical juncture for Japan’s nuclear policy. With more than a dozen reactors slated for shutdown by 2030, the country faces a massive decommissioning backlog. The leak highlights the need for:
- Enhanced transparency and real‑time data sharing with local communities.
- Investment in advanced water treatment technologies capable of handling tritium.
- Revised safety guidelines that reflect the realities of aging infrastructure.
Failure to address these issues could erode public confidence and delay the safe closure of other facilities.
Conclusion
The unexpected tritium‑laden water leak at the Fugen Advanced Thermal Reactor serves as a stark reminder of the hidden risks embedded in nuclear decommissioning projects. While swift containment actions have prevented any immediate health hazard, the episode exposes gaps in preparation, monitoring, and communication. As Japan accelerates the retirement of its nuclear fleet, robust regulatory oversight, upgraded remediation technologies, and transparent stakeholder engagement will be essential to safeguard both the environment and public trust.
| Parameter | Measured value | Regulatory limit |
|---|---|---|
| Tritium concentration (Bq/L) | 1,200 | 150 |
| Detection date | 2025‑12‑22 | — |
| Containment action time | 2 hours | Immediate |
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