Mitsubishi Heavy Industries (MHI) has been selected as the core company in charge of the conceptual design of a demonstration fast reactor which the government aims to put into operation in the 2040s. MHI will oversee both the conceptual design as well as research and development for a sodium-cooled fast reactor in partnership with Mitsubishi FBR Systems (MFBR), an MHI Group engineering company established in 2007 to handle the development and design of fast reactors. The design work for the new reactor is scheduled to begin in fiscal 2024.

The government adopted a "strategic roadmap" for fast reactor development in December 2018, which sought to assess the efficacy of various types of fast reactors to be developed following a technological competition among private-sector corporations. The roadmap was revised in December 2022, at which time two decisions were taken:

  • to select a sodium-cooled fast reactor as the target of the conceptual design which would get underway in fiscal 2024; and
  • to select a manufacturer as the core company in charge of the design and R&D which would proceed with technology development in accordance with the goals and policy directions established by the government.

Japan’s experience with fast reactors has been a difficult one. In June, the Nuclear Regulation Authority (NRA) approved a screening report concluding that the Japan Atomic Energy Agency’s Joyo experimental fast reactor had met new regulatory standards, which were a prerequisite for its restart. A period of public consultation is now underway.

JAEA is hoping 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 operational 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, which finally took place in 2014.

In the report, the NRA confirmed that Joyo is now 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.

In 2007, MHI had been selected as the core company in charge of a research programme which was focused on the practical uses of fast reactors. The selection took into account MHI's technologies and experience based on its participation in the development and construction of the Joyo and reactors. MHI, in partnership with MFBR has since been developing plant conceptual studies and R&D. In view of the lessons learned from the Fukushima Daiichi accident in 2011, MHI proposed the concept of a safety-enhanced sodium fast reactor at the Generation IV International Forum (GIF). Together with JAEA, MHI led a study on global safety standardisation and the results were applied in the joint design and development of France's next-generation fast reactors.

France’s Framatome and the Commissariat a l'energie atomique et aux energies alternatives (CEA – Atomic & Alternative Energies Commission) in 2019 signed a cooperation agreement with JAEA MHI and MFBR. This followed the agreement established in 2014 for the Astrid [Advanced Sodium Technological Reactor for Industrial Demonstration] sodium-cooled fast reactor project, which was subsequently cancelled. In 2022, MHI, JAEA and MFBR also agreed to co-operate with US-based Terrapower on sodium fast reactor technology.

Currently Japan's basic policy of promoting the nuclear fuel cycle is based on reducing the volume and hazard level of highly radioactive waste, effective use of energy resources, and energy self-reliance. MHI said that, going forward, together with MFBR, it “will apply its technologies and experience as it begins the demonstration reactor's conceptual design and its requisite R&D, for the realisation of a fast reactor.”

Image: Cutaway of a tank-type sodium-cooled fast reactor (courtesy of MHI)