US nuclear start-up Antares has signed a long-term enrichment services agreement with Urenco to supply high-assay low-enriched uranium (HALEU) to support Antares’s planned microreactor deployments in North America and allied markets. The fuel will be produced at Urenco’s HALEU enrichment facility under construction at Capenhurst in the UK, which is expected to start producing HALEU by the early 2030s.
HALEU – uranium enriched to 5-20% uranium-235 – is required for most of the next-generation reactor designs currently under development. Currently only Russia and China produce HALEU at scale. In 2024, the UK Government announced funding of £196m ($263m) to Urenco to support construction of a HALEU fuels facility at Capenhurst.
“We are pleased to execute with Antares the world’s first multi-year contract for the supply of HALEU, which marks an important milestone in the maturation of this new market,” said Magnus Mori, Head of Advanced Fuels for Urenco. “With our UK HALEU facility set to come online in 2031, we look forward to a long-term supply relationship supporting the deployment of Antares’ reactor technology.”
Antares, founded in 2023, is developing the R1 microreactor based on a heat-pipe-cooled core and HALEU tristructural-isotropic (TRISO) fuel The heat pipes contain liquid sodium, which heats up near the core, turns into vapor, and flows to the other end where it condenses, heating a secondary system. The liquid sodium then returns to the core by capillary action through a wick structure inside the pipe. The heat generated by the core and transferred by the heat pipes is used to power a closed nitrogen Brayton cycle system. The reactor core uses graphite to both moderate the nuclear reaction and reflect neutrons.
“Microreactors fuelled with HALEU will be more performant and more economical,” said Jordan Bramble, CEO of Antares. “This partnership ensures that when we scale beyond material allocated by the federal government, we will have commercial supply ready to meet our needs.”
Antares has made rapid progress as a result of extensive support from the US Department of Energy (DOE), Department of War and NASA as well as private investment. It has secured contracts with the United States Air Force, Space Force, Defense Innovation Unit (DIU), and NASA and has raised over $130m in funding. It is building a facility in Torrance, California, capable of producing 10 R1 units a year.
The company aims to demonstrate a low-power test reactor before 4 July, in line with President Trump’s May Executive Order 14301 – Reforming Nuclear Reactor Testing at the Department of Energy – and to test its electricity-producing demonstration unit in 2027. Antares says production units will be deployed as early as 2028.
BWX Technologies began fabrication of the TRISO fuel for the initial Antares reactors in 2025. BWXT obtained the initial HALEU feedstock by recycling and downblending US government-owned nuclear scrap material under a contract with DOE’s. The bulk of this scrap material (including uranium enriched to 90% U-235) was collected from the Y-12 National Security Complex in Oak Ridge, Tennessee, which produced material for the weapons programme.
