US-based Terrestrial Energy has executed an Other Transaction Authority (OTA) agreement with the US Department of Energy (DOE) for Project TETRA, which aims to construct and operate a pilot reactor which will support Integral Molten Salt Reactor (IMSR) plant development. This advances Terrestrial Energy’s engagement with the Advanced Reactor Pilot Program, established by Executive Order 14301, under which the Company is targeting IMSR plant deployment facilitated by the DOE’s accelerated authorisation of pilot TETRA reactor operation.
The Advanced Reactor Pilot Program enables the DOE to authorise privately built reactors outside its national laboratories. The program provides a streamlined pathway to regulatory authorisation for operation, bridging the gap between pilot reactor operations for system testing, and licensing for commercial plant operation. In September 2025, Terrestrial Energy was separately selected for the DOE Fuel Line Pilot Program.
Signing an OTA marks the transition from project selection and planning into active execution under DOE authorisation. It establishes a direct, streamlined collaboration with the DOE to review and authorise the design and safe operation of the TETRA reactor, a molten salt-fuelled, graphite-moderated reactor that uses standard assay, low-enriched UF₄-based fuel (SALEU) containing less than 5% U-235. This agreement enables Terrestrial Energy to move quickly from design to operation under DOE authorisation. The OTA enables Terrestrial to operate outside traditional federal contracting constraints, providing a flexible and agile framework designed for swift advanced reactor innovation.
“This OTA is a partnership with the US Department of Energy to accelerate development, licensing, and operation of IMSR plants servicing critical energy needs,” said Simon Irish, CEO of Terrestrial Energy. “The agreement sits on our development centre-path, allowing the company to expedite key elements of its programme to prepare licensing applications for commercial plant operation. The pilot TETRA reactor project affirms our position as a leading advanced reactor innovator and will demonstrate our ability to deliver the innovations necessary for clean, firm and affordable energy in a competitive timeframe.”
The IMSR design is for a 442 MWt per Core-unit (IMSR400) 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).
