Terrestrial Energy has submitted its Thermal and Electric Facility (TEF) Topical Report to the US Nuclear Regulatory Commission (NRC). This seeks to fundamentally change how its Integral Molten Salt Reactor (IMSR) plants are constructed, licensed, and financed.
The IMSR design is for a 442 MWt small modular molten salt fuelled, graphite moderated, thermal spectrum reactor. Terrestrial Energy has developed a two-unit configuration which can deliver 884 MWt/390 MWe. The design features a completely sealed reactor vessel with integrated pumps, heat exchangers and control rods all inside a single vessel. The sealed core-unit is replaced completely at the end of its useful service life (nominally seven years).
The filing splits the IMSR plant into two distinct regulatory pathways:
- The nuclear facility, which contains the core nuclear systems and remains on the standard nuclear licensing timeline; and
- The Thermal and Electric Facility (TEF), which houses the conventional, non-nuclear systems, including the steam supply systems, turbines, and generators.
By asking the NRC to confirm that building the TEF does not constitute “nuclear construction” under federal law, Terrestrial aims to treat the power-generation side as a conventional industrial project. If approved, the TEF can be customised and built before obtaining a nuclear construction permit.
The facility could enter commercial operation early by using an auxiliary heat source such as natural gas to provide electricity and heat to industrial customers before the nuclear reactor is commissioned. An accelerated timeline would shorten the critical path to revenue and provides financing partners with a standard, bankable construction phase.
The report shows that the reactor’s nuclear systems operate independently and do not rely on the TEF for safety, ensuring that any mechanical failure in the generator facility is completely isolated from the nuclear core.
This is the company’s third topical report in 2026, following a graphite qualification report in September and previously approved methodologies for Principal Design Criteria and Postulated Initiating Events. Terrestrial Energy is targeting the early 2030s for the commercial deployment of its fleet across the US. Approved Topical Reports establish foundational elements of the IMSR licensing basis that may be referenced in future applications without re-evaluation, reducing the scope of subsequent technical review.
“This submission can change how an IMSR Plant is regulated, built and financed,” said Simon Irish, CEO of Terrestrial Energy. “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.”
The nuclear technological architecture is progressing through the US regulatory pipeline via a series of approved NRC Safety Evaluation Reports. In September 2025, NRC approved the plant’s Principal Design Criteria, validating the core safety logic of the Gen IV liquid-salt approach. Approval of the Postulated Initiating Events (PIE) methodology followed in May. This formally certified that the reactor’s inherent physics can safely handle extreme operational emergencies.
In September, the company submitted its Graphite Qualification Methodology Topical Report to NRC establishing the technical foundation for how the reactor’s structural graphite components withstand continuous high-temperature molten salt exposure.
A major competitive advantage established by Terrestrial Energy is designing the IMSR to run on Standard-Assay Low-Enriched Uranium (SALEU) enriched to less than 5% U-235. Most other Generation IV SMRs rely on high-assay LEU (HALEU), which currently faces severe global supply-chain constraints.
The company has finalised supply contracts with major global fuel manufacturers including Orano, Urenco, and Westinghouse, with the aim of guaranteeing a commercially viable rollout using standard infrastructure.
