Fugen was not an import. While most of Japan's commercial reactors followed American light-water designs, Fugen was a domestically conceived Advanced Thermal Reactor -- heavy water moderated, boiling light water cooled -- designed to demonstrate that Japan could develop its own path in nuclear energy. The reactor produced 165 megawatts of electrical output from 557 megawatts of thermal power. It achieved first criticality in 1978 and began generating electricity on March 20, 1979. Its signature achievement was becoming the first reactor in the world to operate with a full core of MOX fuel -- a blend of plutonium and uranium oxides recovered from spent nuclear fuel. With 772 fuel assemblies, the most of any reactor using this technology, Fugen proved that plutonium recycling was technically feasible on a commercial scale.

The record was not clean. In April 1997, a tritium leak occurred at the facility. Management waited 30 hours before reporting it to the authorities. The ensuing investigation revealed that this was not an isolated lapse -- 11 similar incidents had gone unreported. Five managers of the Power Reactor and Nuclear Fuel Development Corporation, Fugen's operator, resigned. The pattern of concealment rattled public trust in Japan's nuclear establishment, foreshadowing larger scandals at other facilities in the years to come. In April 2002, roughly 200 cubic meters of steam escaped from a defective pipe, and the reactor was shut down. By then, the Advanced Thermal Reactor concept had been judged obsolete, overtaken by other designs. Fugen ceased operations on March 29, 2003, having run for exactly 24 years.

Decommissioning began formally in February 2008, when the Japan Atomic Energy Agency reorganized the facility into the Fugen Decommissioning Engineering Center. The process started with the least contaminated components -- turbine systems and auxiliary equipment -- while researchers developed methods for handling the reactor's unique heavy-water systems. During dismantling, inspectors discovered that structural walls at control points lacked the required strength at 25 of 34 locations tested. In December 2025, a leak of tritium-containing water was again reported at the site, a reminder that decommissioning a nuclear facility is measured in decades, not years. The used fuel itself is being shipped to France, where Orano has been contracted to reprocess it.

Fugen sits on the Tsuruga Peninsula along Wakasa Bay, a stretch of coastline that became one of the densest concentrations of nuclear facilities in the world. The neighboring Tsuruga Nuclear Power Plant, the Monju fast-breeder reactor, and the Mihama plant all cluster within a few dozen kilometers. Locals sometimes call this coast Japan's nuclear alley. The concentration brought jobs and infrastructure to rural Fukui, but also unease -- particularly after the Monju sodium leak in 1995 and the Fukushima disaster in 2011 prompted national soul-searching about nuclear safety. Fugen's bodhisattva namesake promised compassion. What the reactor delivered was more complicated: a genuine technical achievement wrapped in institutional failures, now slowly being taken apart on a coast where the Sea of Japan meets the machinery of the atomic age.