The US Department of Energy (DOE) has approved the Nuclear Safety Design Agreement (NSDA) for nuclear energy start-up Antares Nuclear’s Mark-1 microreactor. This establishes the formal safety standards, design requirements, and regulatory framework that will govern the reactor through its upcoming construction and testing phases.
Mark-1 is designed for sustained power production, unlike its predecessor, Mark-0, which achieved zero-power criticality in June to verify core physics without generating electricity. It integrates a full-scale core and TRISO fuel with a nitrogen closed Brayton cycle power conversion system.
Mark-0 was the first several advanced reactors racing to go critical by the 4 July deadline set by President Trump in his May 2025 Executive Order (EO)14301, Reforming Nuclear Reactor Testing at the Department of Energy. The EO created the DOE Reactor Pilot Program and mandated that the Secretary of Energy approve a streamlined regulatory pathway for at advanced test reactors.
Following the NSDA approval, Antares is on track to operate the Mark-1 at full electrical power for several months at the Idaho National Laboratory (INL) in 2027. Initial field deployments are slated for US military installations beginning in 2028, including plans for a commercial reactor under Project Janus at Fort Bragg in North Carolina.
The NSDA approval marks the second time in a year that Antares has initiated DOE’s authorisation process for a reactor. Mark-0 moved from NSDA approval in October 2025 to criticality in eight months, receiving DOE approval of its Preliminary Documented Safety Analysis and Documented Safety Analysis along the way. Mark-1 if following the same sequence.
In August, Antares was selected for the DOE’s Nuclear Energy Launch Pad Program, led by the Office of Nuclear Energy and the National Reactor Innovation Center (NRIC). This enables Antares to further pursue DOE authorisation to operate nuclear reactors and fuel cycle facilities beyond the National Laboratories, with access to specialised nuclear expertise at INL and other National Labs to assist in navigating DOE authorisation, a flexible contracting framework, and the ability to leverage unique regional and project-specific advantages.
“Mark-0 proved we could take a reactor from a paper design to a self-sustaining chain reaction on the timeline we promised,” said Jordan Bramble, CEO & Co-Founder of Antares. “Mark-1 isn’t a scaled-down, stand-in test rig. It’s commercially representative of the plant we’ll deploy to Fort Bragg under the Army Janus program in 2028. Mark-1 will be the first full-scale electricity-producing microreactor test in the United States. Operating at full electrical power for six months gives us comprehensive test data on every major subsystem and how they behave together. DOE’s approval of this safety agreement is the gate that lets us move not only from neutrons to electrons, but to customer plants, on schedule.”
Antares has also just finalised a major fuel fabrication agreement with BWX Technologies (BWXT). Antares has signed a commercial agreement with BWXT to procure TRISO fuel fabricated from high-assay low-enriched uranium (HALEU) for its microreactors through the end of the decade. The fuel will be produced at BWXT’s facility in Lynchburg, Virginia, on the same fabrication line that made the fuel for the Department of War’s Project Pele and for the Mark-0 and Mark-1 reactors.
The agreement sets terms for an initial allocation of 1 tonne of uranium with the ability to increase as Antares’s deployment schedule requires. Antares now has two qualified sources for the fuel for reactor deployments. It is the company’s second TRISO fuel fabrication agreement, following its earlier agreement with Standard Nuclear.
“BWXT’s decades of experience in advanced fuel manufacturing give us the foundation to support Antares as they accelerate toward commercial deployment,” said Joe Miller, president, BWXT Government Operations. “Our team has refined the processes, tooling and quality systems needed for high-performance TRISO fuel, and this agreement enables us to apply those strengths in a sustained, predictable way. As demand grows across the advanced reactor sector, BWXT is prepared to scale responsibly and reliably.”
Antares, backed by over $600m in funding, is heavily integrated with US defence initiatives. Antares was selected under the Advanced Nuclear Power for Installations (ANPI) framework in April to bring a mobile prototype microreactor to the Joint Base San Antonio in Texas. Active development funding runs to March 2027 to finalise the prototype designs, mapping toward the wider Air Force initiative to have operational on-base power running by 2030 at the absolute latest (with developers actively tracking for a 2028 deployment).
In August, Antares was contracted by the Defense Innovation Unit (DIU) to build, own, and operate three R1 microreactors at Fort Bragg in North Carolina under the Army’s $2.2bn Janus Program. Driven by Executive Order 14299, the contract mandates that Antares must have its R1 microreactors built, factory-delivered, and fully operational by 30 September 2028.
In September, the company also secured a $161m Strategic Breakthrough award from the US Space Force to develop space-qualified reactors, aiming to provide persistent orbital power for advanced military satellites. The ultimate contract timeline dictates a targeted 2028 space launch to power an active, operational ground-to-space defence asset, helping to close a decades-long orbital power gap. The architecture proven by this 2028 space run is intended to lay the groundwork for future deep-space propulsion and eventual lunar surface deployment by 2030.
Both the Army’s Project Janus (Fort Bragg) and the Air Force’s ANPI Initiative (Joint Base San Antonio) utilise a strict milestone-based payment model. Rather than issuing upfront grants or traditional cost-plus contracts, the Department War only releases government funding to Antares after the company successfully hits and verifies defined technical goals. Because payments are tied entirely to execution milestones, vendors like Antares are required to inject significant amounts of their own private capital investment alongside the government funds to hit their targets.
