Japan’s experimental fast reactor, Joyo, in Oarai Town, Ibaraki Prefecture, has secured consent from local governments to begin the safety construction work necessary before it can restart. Joyo’s operator, the Japan Atomic Energy Agency (JAEA), is aiming to restart the reactor in the second half of fiscal 2026 after completing safety construction work, including measures related to cooling and countering accidents.
JAEA hopes to use the experimental reactor for research and development of fast reactors and also plans to offer the reactor for the production of medical radioisotopes.
The sodium-cooled fast reactor began operation in 1977, and is Japan’s only fast reactor since the closure of Monju in 2016. Monju, which achieved criticality in 1994, was shut down in 1995 after a sodium coolant leak and fire. It was restarted in 2010 but was shut down three months later after a fuel handling machine was accidentally dropped into the reactor during a refuelling outage. Joyo was shut down in 2007 after a test sub-assembly became jammed in the reactor vessel. Special equipment had to be designed to retrieve it, an operation that finally took place in 2014.
In 2023 Japan’s Nuclear Regulation Authority approved a screening report concluding that the Joyo experimental fast reactor met new regulatory standards, which are a prerequisite for its restart. In the report, the NRA confirmed that Joyo is equipped with a device to detect sodium leaks, as well as nitrogen gas equipment to be used in the event of such leaks. It concluded that the reactor met fire safety standards.
