Japan’s regulator report allowing restart of Joyo fast reactor

30 June 2023

Japan’s Nuclear Regulation Authority (NRA) has approved a screening report concluding that the Japan Atomic Energy Agency’s Joyo experimental fast reactor has met new regulatory standards, which are a prerequisite for its restart. The report will be formalised after a public comment period.

The JAEA aims to restart Joyo, located in the town of Oarai, Ibaraki Prefecture, at the end of fiscal 2024. 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 subassembly became jammed in the reactor vessel Special equipment had to be designed to retrieve it, which finally took place in 2014.

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 meets fire safety standards.

Image: Aerial view of the Joyo fast reactor in Tokai (courtesy of NRA)

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