Japan's Agency for Natural Resources & Energy (ANRE – part of the Ministry of Economy, Trade & Industry) has selected Mitsubishi Heavy Industries (MHI) as the core company to lead development of a high temperature gas-cooled reactor (HTGR) programme. MHI will coordinate R&D, design, and construction of the HTGR demonstration reactor that ANRE plans to put into operation in the 2030s.

HTGRs produce thermal energy of approximately 1000°C using ceramic (such as silicon carbide) coated fuels and chemically inert helium gas coolant. The Japan Atomic Energy Agency (JAEA -formerly the Japan Atomic Energy Research Institute) began research and development of HTGRs for the multi-purpose use of nuclear/thermal energy in 1969. One result of these efforts was the High Temperature Engineering Test Reactor (HTTR). MHI has also been pursuing development of HTGRs since the 1970s, and accumulated technologies through its role as the principal company for the construction of the HTTR.

The 30 MWt graphite-moderated helium gas-cooled HTTR achieved first criticality in November 1998 and reached full power operation in 2001. It demonstrated stable heat at 950°C over 50 days in 2010. Its fuel is ceramic-coated particles with low-enriched (average 6%) uranium incorporated into hexagonal graphite prisms, giving it a high level of inherent safety. It is designed to establish a basis for the commercialisation of second-generation helium-cooled plants running at high temperatures for either industrial applications or to drive direct cycle gas turbines.

While the HTTR was not severely damaged during the 2011 earthquake and tsunami that destroyed the Fukushima Daiichi NPP, it was still required to meet the stricter regulatory requirements and was taken offline to make the required changes. The reactor resumed operation in July 2021.

Japan’s Strategic Energy Plan adopted in October 2021 outlined a policy for the development of technologies for hydrogen production using HTGRs. In addition, the Green Growth Strategy Through Achieving Carbon Neutrality in 2050 formulated in June 2021 outlined a policy for the development by 2030 of technologies to produce large-scale, low cost, carbon-free hydrogen by utilising HTGRs.

Based on these national policies, in February 2022, ANRE began accepting bids for its Hydrogen Production Demonstration Project Utilising Very High Temperature. A consortium comprising JAEA, and MHI were selected for this project. MHI headed the design and construction group of this project and has developed software technologies to verify the performance and integrity of the reactor core and other high temperature structures. It also developed hardware technologies such as manufacture of high-temperature structures and heat exchangers.

Since April 2022, MHI has also participated in a demonstration programme to produce hydrogen using the HTTR in partnership with JAEA. The aim is to connect a hydrogen production plant to the HTTR as part of a demonstration test for hydrogen production.

They will formulate a development plan for equipment such as high temperature isolation valves in preparation for a demonstration reactor. JAEA and MHI will also analyse technologies for carbon-free hydrogen production capable of using high temperature heat from HTGRs, and compare these technologies to determine hydrogen production methods with the potential to enhance the efficiency of hydrogen production.

MHI is now developing hydrogen production technology for the multi-purpose use of the HTGR, and the helium gas turbine direct power generation system for high efficiency power generation. These technologies will be the key to the future commercialisation of HTGRs. MHI is also developing a gas-turbine system for the high-temperature gas power reactor PBMR project of South Africa’s PBMR Co.

Image: Illustration of a hydrogen terminal utilizing an HTGR (courtesy of MHI)