The Integrated Molten Salt Reactor (IMSR) is a Generation IV reactor that uses molten salt as both fuel and coolant, with integrated components, which can supply heat directly to industrial facilities or use it to generate electrical power. The plant itself is designed in two discrete parts: the Nuclear Facility, which contains standardised and modular nuclear systems, and the Thermal and Electric Facility, or TEF, containing non-nuclear heat transfer, steam supply and electric systems for commercial power generation and thermal energy supply.
In its submission, Terrestrial Energy asks the US Nuclear Regulatory Commission (NRC) to confirm that building the TEF is not “nuclear construction” under US regulations. The submission incorporates elements of the company’s Postulated Initiating Events methodology, already approved by the NRC. Terrestrial Energy says it shows that the plant’s nuclear systems do not rely on the TEF for safe operation and that any failure originating in the TEF is isolated from the nuclear systems.
Topical Reports establish foundational elements of the licensing basis that may be referenced in future applications without re-evaluation. NRC approval of the TEF Topical Report would mean the TEF, which could be customised for each site, could be built and operated using an auxiliary heat source such as natural gas as a bridge to nuclear power ahead of a nuclear construction permit and operating licence being granted for the nuclear part of the plant.
“This submission can change how an IMSR Plant is regulated, built and financed,” Terrestrial Energy CEO Simon Irish said. “With its NRC approval, only the nuclear portion of the plant would follow the nuclear licensing timeline. The rest of the plant would become a conventional industrial project, giving customers earlier power and heat and giving financing partners a bankable construction phase. As this pathway applies to every IMSR Plant, it is a fleet-wide advantage, not a one-off exemption.”
Terrestrial Energy says it is developing a pipeline of IMSR Plant projects, including plans for a plant at the Texas A&M-RELLIS site in Bryan, Texas. In September, the company announced its selection as supplier of advanced nuclear plant technology for Ameresco Inc’s power plant project at the US Army’s Aberdeen Proving Ground in Maryland, following a competitive request for proposals and selection process.
The NRC has been engaged with Terrestrial Energy in pre-application activities for the IMSR since 2019. This is the third of at least five Topical Reports the company is aiming to submit to the regulator during 2026.
