The US Department of Energy (DOE) has approved cost-shared funding for an accelerated final stage of the Molten Chloride Reactor Experiment (MCRE) under its Advanced Reactor Demonstration Program (ARDP). The project is a collaborative effort involving Southern Company, Idaho National Laboratory (INL), and UK-based start-up Core Power.
MCRE is designed to become the first fast-spectrum molten chloride salt reactor experiment to reach criticality. The experiment is projected to achieve first criticality as early as 2027. Until now, fast-spectrum molten salt behaviour has relied purely on models. The project will generate empirical data on fuel behaviour, reactor physics, and overall performance.
Data from MCRE will lay the groundwork for licensing pathways and future commercial deployment of TerraPower’s Molten Chloride Fast Reactor (MCFR) design. INL previously achieved a major milestone by streamlining the sustainable production of the necessary uranium chloride fuel salt matrices for MCRE.
The public-private partnership that originally committed to the project in 2020 consists of DOE working alongside a core consortium of industry leaders:
- Southern Company (acting as the prime recipient and project lead);
- TerraPower (providing the core Molten Chloride Fast Reactor design);
- Core Power (focusing on maritime and industrial system deployment); and
- INL (hosting the reactor experiment and synthesizing the fuel).
The alliance was solidified in December 2020 when the DOE selected the consortium’s proposal under the ARDP Risk Reduction pathway. While the team also collaborates with technical groups including Orano Federal Services, the Electric Power Research Institute (EPRI), and 3M, the core partnership remains anchored by Southern Company, TerraPower, Core Power, and the DOE.
In August 2023, DOE issued its final environmental assessment and finding of no significant impact, clearing the project to proceed. In September 2025, INL delivered the first baseline batch of enriched uranium chloride fuel salt and by March had completed the production of four subsequent major development batches of the fuel matrices.
DOE has now approved the cost-shared funding injection to accelerate the final development stage toward criticality, which is now targeted for 2027. Operations are then set to begin at the Laboratory for Operations & Testing in the US (LOTUS) test bed at INL’s Materials and Fuels Complex.
The experiment will run for a planned six-month empirical data window before being decommissioned. The empirical data harvested during the MCRE trials will formally guide commercial and maritime deployment of TerraPower’s full-scale Molten Chloride Fast Reactor (MCFR) planned to begin operation in the 2030s.
The total estimated cost for the MCRE project is approximately $170m. DOE is funding 80% of the project cost through ARDP. The remaining 20% is cost-shared by the private consortium led by Southern Company, TerraPower, and Core Power.
To reach first criticality by 2027, the project must complete the following major technical and regulatory milestones:
- Fuel production completion (2025–2026): Idaho National Laboratory (INL) must finish processing the remaining batches of the specialised enriched uranium chloride fuel salt matrix.
- LOTUS facility modification (2026): Upgrades must be finalised at LOTUS, the heavily shielded test bed where the experimental reactor core will be housed.
- Final safety authorisation (early 2027): DOE must issue its final safety design authorisation to permit the loading of live fuel into the reactor assembly.
- Core assembly & cold testing (mid-2027): Physical installation of the reactor components will be followed by mechanical, thermal, and hydraulic testing using non-nuclear surrogate salts.
- Fuel loading & criticality (late 2027): Uranium chloride fuel must be loaded into the reactor to initiate the self-sustaining nuclear chain reaction for the first time.
“MCRE will be the world’s first fast-spectrum molten chloride reactor to achieve criticality,” said Jess Gehin, INL Associate Laboratory Director for Nuclear Science & Technology. “It will provide direct measurements of how this novel reactor behaves during sustained fission, data that until now, has come from models alone. Enhancing those models with real-world operating evidence will reduce uncertainty for future reactor designers and regulators.”
Dr Mark S Berry, Southern Company Senior Vice President for Research, Environment & Sustainability said public-private partnerships are essential role to advance energy technologies from concept to demonstration. “Through collaboration among DOE, Idaho National Laboratory and industry partners, MCRE will help expand knowledge of molten salt reactor technology and help reduce technical uncertainty for future developers,” he noted.
Core Power CEO Mikal Bøe said: “The data generated by this unique experiment will help determine how we develop engineering, licensing and an entirely new supply chain to practical commercial deployment of fast-spectrum molten salt reactors…. Merging the pathway of novel nuclear fuel cycle development that MCRE represents with Core Power’s pathway of maritime nuclear development, creates unique opportunities to deliver an ultimately sustainable nuclear fuel solution to new markets around the world.”
