Antares Nuclear achieved initial criticality of its Mark-0 microreactor at Idaho National Laboratory on June 4, powered by TRISO fuel manufactured by BWX Technologies — the first privately developed non-light water reactor to reach that milestone in more than four decades.
Antares Nuclear achieved initial criticality of its Mark-0 microreactor at Idaho National Laboratory on June 4, powered by TRISO fuel manufactured by BWX Technologies — the first privately developed non-light water reactor to reach that milestone in more than four decades.
BWX Technologies' TRISO nuclear fuel powered Antares Nuclear Inc.'s Mark-0 microreactor through initial criticality at Idaho National Laboratory, marking the first privately developed non-light water reactor to achieve the milestone in more than 40 years.
"This marks a historic milestone for advanced nuclear fuel fabrication in the United States," U.S. Energy Secretary Chris Wright said. "The Trump administration is proud to partner with private companies such as BWXT, as we strengthen the foundation of a reliable and secure nuclear supply chain."
The criticality test, conducted under Executive Order 14301 and the DOE Reactor Pilot Program, used TRISO (TRi-structural ISOtropic) fuel compacts manufactured at BWXT's Specialty Fuels Fabrication facility in Lynchburg, Virginia. BWXT also processed the high assay low enriched uranium (HALEU) feedstock — enriched to 19.75% uranium-235, compared with 3% to 5% for conventional reactor fuel — from scrap materials provided by the National Nuclear Security Administration. Antares modeled its fuel on the specification developed through Project Pele, the 1.5 MW transportable microreactor BWXT is building for the U.S. Army's Strategic Capabilities Office.
The demonstration validates a replicable licensing pathway that DOE and industry can use to accelerate future reactor tests on commercial timelines. Antares expects to produce electricity from the same facility in 2027 and deliver power to U.S. military installations by September 2028, according to CEO Jordan Bramble.
The achievement positions BWXT as a critical supplier across the full spectrum of advanced nuclear fuel production, from HALEU processing to TRISO fuel fabrication. The company reported $861.1 million in revenue for the first quarter of 2026 and held an $8.7 billion backlog, according to its latest filings. Its gross margin stood at about 23% for the quarter ended March 31.
A Fuel Specification Decades in the Making
The TRISO fuel specification used in the Mark-0 was developed within DOE's Advanced Gas Reactor program over several decades. Each TRISO particle — roughly the size of a poppy seed — contains a uranium kernel surrounded by three layers of carbon- and ceramic-based materials that act as a containment system, making it one of the most robust nuclear fuel designs in existence. Antares went from concept to a critical reactor in less than 12 months, Bramble said. The company, founded in 2023 and backed by more than $140 million in funding, operates facilities in Torrance, California; Idaho Falls, Idaho; and Aiken, South Carolina.
Competitive Implications for the Nuclear Supply Chain
BWXT's ability to manufacture TRISO fuel from recycled NNSA scrap materials demonstrates cost efficiency and supply chain resilience that competitors may struggle to match. Oklo, another advanced nuclear developer, remains in a pre-revenue stage and reported negative free cash flow of $50.7 million in the first quarter of 2026, according to its filings. BWXT, by contrast, generates consistent revenue from its near-monopoly position powering the U.S. Navy's submarine and aircraft carrier fleet, and recently secured $1.4 billion in new contracts under the Naval Nuclear Propulsion Program. The company's acquisition of Precision Components Group further expands its capabilities into commercial nuclear manufacturing, diversifying beyond defense contracts.
BWXT shares trade with a market premium reflecting its entrenched government contracts and growing commercial nuclear business. The Antares milestone, if it leads to follow-on fuel orders for electricity-producing reactors, could expand BWXT's addressable market beyond defense into the commercial advanced reactor sector — a shift that would test whether the company's manufacturing capacity can scale to meet both military and civilian demand.
This article is for informational purposes only and does not constitute investment advice.
