The Japan Atomic Energy Agency (JAEA), Mitsubishi Heavy Industries (MHI), Mitsubishi FBR Systems (MFBR), and US-based TerraPower have expanded their January 2022 Memorandum of Understanding (MOU) on the development of sodium-cooled fast reactor (SFR) technologies.

Japan's government in December 2018 adopted a strategic roadmap for fast reactor development whereby it would assess the efficacy of various types of fast reactors following a technological competition among private-sector corporations. The roadmap was revised in December 2022, at which time two decisions were taken. The first was to select a SFR as the basis of the conceptual design of the demonstration reactor to begin in fiscal 2024. The second was to select a manufacturer as the core company in charge of the design and R&D in accordance with the goals and policy directions established by the government.

In July, MHI was selected by the Japanese government to lead the conceptual design of a demonstration 650 MWe pool-type, SFR for operation in the 2040s. MHI is to oversee both the conceptual design as well as research and development for the reactor in partnership with MFBR. It is hoped that the concept will be finalised by around 2030.

Under the expanded MOU, TerraPower and Japan will consider collaborating on a common reactor design concept, based on the Japan's FR demonstration programme and TerraPower's existing technologies. This MOU has been revised to include an increase in size for Terrapower’s Natrium design to improve cost competitiveness and metal fuel safety.

TerraPower is currently developing its 345 MWe Natrium reactor design in the US supported by the US Department of Energy (DOE) through its Advanced Reactor Demonstration Program (ARDP). The first Natrium plant aims to begin commercial operations in 2030. The company has selected Kemmerer in Wyoming as the preferred site for the Natrium demonstration project, which will feature a SFR with a molten salt-based energy storage system. The storage technology is designed to temporarily boost the system's output to 500 MWe when needed, enabling the plant to follow daily electric load changes and integrate seamlessly with fluctuating renewable resources.

"We are thrilled to expand our collaboration with JAEA as Japan works to bring advanced nuclear reactors to market," said TerraPower President and CEO Chris Levesque. "In order to achieve our climate goals, countries across the world are going to need to deploy advanced reactors starting in the 2030s, and this agreement will help us evaluate the design opportunities for large-scale Natrium plants that can support Japan's carbon targets."

Japan's Strategic Roadmap for FR technology identifies the SFR as one of the most promising technologies and emphasises the importance of international cooperation. JAEA President Masanori Koguchi said, JAEA will play a role as one of organisations in the strategic roadmap for fast reactor development. “For effective development, we believe that international cooperation is one of the key issues,” he said. “We will promote Japan-US collaboration on FR development through this expanded MOU."

MHI Executive Vice President Akihiko Kato said, "MHI group, as the core company in charge of design and development of the Japanese demonstration fast reactor, will steadily proceed in accordance with the strategic roadmap. We would like to contribute to fast reactor development cooperation between the US and Japan by utilising the technology and experience we have cultivated over many years."

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

Image: The Japan Atomic Energy Agency's Monju fast-breeder reactor in Tsuruga, Fukui Prefecture