US nuclear start-up Antares has raised $96m in a Series B funding round led by Shine Capital, with participation from Alt Capital, Caffeinated, FiftyThree Stations, Industrious, and other investors. The round comprises $71m in new equity capital and $25m in debt for equipment, factory build-out, and uranium procurement.
Antares CEO Jordan Bramble said funding marks a major milestone for Antares. “We’re months away from our first reactor demonstration, which will validate our control systems and neutronics models, develop our testing facility, and fabricate our fuel ahead of our full upcoming scale electricity producing prototype in 2027. We’ve raised the capital we need to mobilise to provide resilient energy for our partners at the Department of War (DOW) and NASA.”
Antares, founded in 2023, is developing the R1 microreactor based on a heat-pipe-cooled core and 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 back into the core to increase efficiency.
The system is designed for autonomous and reliable operation in remote environments, featuring automated controls for power management and distribution, reducing the need for a specialised on-site workforce. It is designed to be highly transportable, capable of being moved on standard trucks and quickly deployed with minimal specialised equipment.
Antares has made rapid progress as a result of extensive support from the Department of Energy (DOE), DOW and NASA as well as private investment. Antares 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 2026, 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.
Antares announced an $8m seed round in October 2023. In March 2024 it formed a Strategic Partnership Project with Battelle Energy Alliance, operator of the Idaho National Laboratory (INL). Shortly after it demonstrated its first sodium heat pipe. A Co-operative Research & Development Agreement was signed with Savannah River National Lab in September 2024. The same month Antares was awarded $3.75m in Department of Defense Funding (three Small Business Innovation Research awards with the US Air Force) as well as a DOE Gateway for Accelerated Innovation in Nuclear (GAIN) voucher to support its core design work with Oak Ridge National Laboratory.
In October Antares partnered with INL and the National Reactor Innovation Center (NRIC) front-end engineering & experiment design (FEEED) program in preparation for testing at the DOME facility at INL. It also secured $30m in a Series A funding round.
In February 2025, Antares opened its factory in California for research and development, component manufacturing, and ultimately assembling its first microreactors. In April, Antares was selected by DIU under the Advanced Nuclear Power for Installations (ANPI) program to provide nuclear power to DOW installations.
July saw two new contracts signed with INL to support the next phases of their reactor development including some $40m to build and demonstrate the R1 microreactor in an existing facility at INL. In August Antares was selected for DOE’s Nuclear Reactor Pilot Program and DOE allocates HALEU Fuel to Antares Microreactor Project. In September Antares executed agreement with DOE to take its reactor critical by July 2026 and in October DOE approved its Nuclear Safety Design Agreement.
Announcing the latest $96m funding round, Bramble noted: “The US had lost the ability to build nuclear hardware quickly and iteratively. For nearly half a century, nuclear engineering became dominated by paperwork and modelling – designs, analyses, and reviews – without the develop-build-test-iterate cycles required to mature real systems. Entire generations of engineers retired without ever building or operating the hardware they spent their careers designing. We raised this round to change that trajectory.”
He added: “The capital raised today positions us to compete in several sector-defining federal programmes across the Department of the Army, NASA, and other federal agencies…. Over the long term, our goal is simple: abundant energy throughout the Solar System…. With this fundraise, we move one step closer to that vision.
