US firm to build Gen IV nuclear reactor that uses molten salt as both fuel and coolant
US-based Terrestrial Energy has executed an Other Transaction Authority (OTA) agreement with the Department of Energy (DOE) for Project TETRA. This project involves the construction and operation of a pilot nuclear reactor to support the development of the company’s Integral Molten Salt Reactor (IMSR).
The OTA provides a framework for the DOE to review and authorize the design and operation of the TETRA reactor. This system is a molten salt-fueled, graphite-moderated reactor that uses standard assay, low-enriched uranium fuel containing less than five percent U-235.
The agreement allows the project to proceed under DOE oversight rather than traditional federal contracting structures, intended to facilitate the transition from design to physical operation.
Project to demonstrate capabilities of molten salt reactors
The pilot project is intended to validate the technology required for commercial IMSR plants. According to company officials, the agreement supports the preparation of licensing applications for future commercial operation.
The project aims to demonstrate the capability of molten salt reactors to provide energy for electricity and industrial heat within a specified timeframe.
“Operating at 44 percent thermal efficiency (net), an IMSR cogeneration plant can generate 392 megawatts of electricity from 884 megawatt of thermal reactor power,” highlighted the company.
By using molten salt as both fuel and coolant, the system operates at higher temperatures and lower pressures than conventional water-cooled reactors.
This stability allows for the delivery of heat at 1292°F (700°C), which can be used directly for industrial processes such as chemical synthesis or data center operations.
Distinct design from other advanced reactors
The decision to use standard assay low-enriched uranium (SALEU) distinguishes this design from other advanced reactors that require high-assay low-enriched uranium (HALEU).
Because SALEU is currently used by the existing nuclear fleet, the company can utilize established US manufacturing infrastructure and avoid the supply chain constraints associated with HALEU.
This fuel choice is intended to support the scalability of the technology for near-term deployment.
To address the limited lifespan of graphite moderators in high-power reactor cores, the IMSR integrates primary components into a sealed core-unit.
This unit has an estimated operating life of seven years and is designed to be replaced as a single module. This approach is intended to manage the degradation of the graphite without requiring complex on-site maintenance of the internal reactor structures.
Integration with federal energy programs
The initiative is part of the Advanced Reactor Pilot Program, which seeks to accelerate the authorization and deployment of advanced nuclear plants. The program provides a pathway for the DOE to authorize privately built reactors outside of national laboratories.
This program is designed to bridge the gap between pilot testing and commercial licensing for advanced nuclear systems. In addition to Project TETRA, Terrestrial Energy was selected for the DOE Fuel Line Pilot Program in September 2025.
These combined efforts are part of a broader strategy to deploy small modular reactors that serve as an alternative to fossil fuels for industrial thermal energy and power generation.