Fugen ふげん was a prototype Japanese nuclear test reactor. Fugen was a domestic Japanese design for a demonstration Advanced Thermal Reactor. It was a heavy water moderated, boiling light water cooled reactor. The reactor was started in 1979 and shut down in 2003. As of 2018, it is undergoing decommissioning. It is located in Myōjin-chō, in the city of Tsuruga, Fukui. The name "Fugen" is derived from Fugen Bosatsu (Samantabhadra), a Buddhist deity.