Antares Wins DOE Safety Design Approval for Mark-1, Its First Electricity-Producing Microreactor
Antares Nuclear has cleared the first regulatory step toward generating electricity from a privately built microreactor in the United States. The Torrance, California-based developer said Oct. 23, 2026, that the U.S. Department of Energy approved the Nuclear Safety Design Agreement for Mark-1, its first electricity-producing reactor, which the company plans to operate at full electrical power for several months in 2027 at Idaho National Laboratory before supplying reactors to military customers from 2028.
Key developments
- DOE approved the Nuclear Safety Design Agreement (NSDA) for Mark-1, the first gate in the department's authorization pathway. The agreement sets the design requirements, safety analysis approach and regulatory expectations that will govern construction and operation.
- Mark-1 will pair the reactor with a nitrogen closed Brayton cycle power conversion system and is scheduled to run at full electrical output for several months in 2027 at Idaho National Laboratory.
- The unit reuses the full-scale core, TRISO fuel and test facility of Mark-0, the company's demonstration reactor that reached zero-power criticality on June 4, 2026.
- This is the second NSDA Antares has received in 12 months. Mark-0 moved from NSDA approval in October 2025 to criticality in about eight months.
- Antares said data from the 2027 campaign will support initial deliveries to defense customers beginning in 2028, including the first of several reactors at Fort Bragg, North Carolina, under the U.S. Army's Janus program.
How the authorization pathway works
Reactors tested under DOE authority at national laboratories follow a staged safety review rather than a commercial Nuclear Regulatory Commission license. The NSDA is the opening document in that sequence. It fixes the safety basis a developer must meet before DOE reviews preliminary and final documented safety analyses and ultimately permits fuel loading and operation. Antares followed the same path with Mark-0, receiving DOE approval of its preliminary documented safety analysis in January 2026 and its final documented safety analysis in April, according to the company's update log.
Mark-0 was the first of four advanced reactors to reach criticality under DOE's Reactor Pilot Program, which an executive order tasked with getting at least three test reactors critical by July 4, 2026. DOE reported in July that Valar Atomics, Deployable Energy and Aalo Atomics also reached criticality, exceeding that target. The Army said Mark-0 operated at Idaho National Laboratory's Materials and Fuels Complex, the former site of the Army's Mobile Low Power-1 reactor. A zero-power test proves a core can sustain a chain reaction but produces no usable electricity. Mark-1 is the step that adds heat removal, power conversion and sustained operation.
Antares CEO Jordan Bramble said Mark-1 will be the first full-scale electricity-producing microreactor test in the United States and described it as commercially representative of the plant planned for Fort Bragg. The company has not disclosed the unit's electrical rating.
Industry implications
The approval matters because the advanced reactor sector has long struggled to move from criticality demonstrations to power-producing hardware. Several developers have now shown that a core can go critical. Far fewer have shown that a complete system can convert heat to electricity reliably over months. A full-power campaign in 2027 would give Antares operating data on fuel behavior, heat transport and Brayton cycle performance that customers and regulators expect before deployment.
Timing also aligns with a regulatory shift at the commercial level. The American Nuclear Society reported Oct. 22 that the NRC finalized a rule allowing applicants whose designs were already authorized by DOE or the Department of Defense to rely on that analysis and test data in a streamlined commercial review, with target review times of about 18 months for first-of-a-kind applications and 12 months for later units. If that framework works as intended, data generated under DOE authority at Idaho could shorten the path from a military prototype to civilian sales.
Competitive and supply chain implications
The Army's Janus program sets the competitive frame. In August, the Army and the Defense Innovation Unit selected five vendors for up to a combined $2.2 billion in milestone-based awards funded from fiscal 2027 through 2031: Antares at Fort Bragg, BWXT Advanced Technologies at Fort Campbell, General Atomics Electromagnetic Systems at Fort Hood, Radiant Industries at Fort Benning and Westinghouse Government Services at Fort Drum. Vendors will own, build and operate the reactors and receive government money only after hitting technical milestones. The Army is targeting September 2028 for its first Army-regulated reactor operating on an installation.
Under that structure, an early full-power test is a commercial asset as much as a technical one. Antares has also been locking in fuel, the most constrained input for advanced reactors. Its update log lists high-assay low-enriched uranium supply agreements with Urenco in May, General Matter in July and Centrus in September, plus a multi-year TRISO fuel supply agreement with Standard Nuclear in August. The company raised a $470 million Series C round in July, and it was selected in September for a $161 million Strategic Breakthrough Award to demonstrate a space reactor.
Regional implications
Idaho remains the center of gravity for U.S. advanced reactor testing. Antares opened an Idaho Falls office in November 2025, and both Mark-0 and Mark-1 rely on Idaho National Laboratory infrastructure as more developers compete for the lab's test bays and review capacity.
North Carolina stands to host one of the first operating military microreactors if the Fort Bragg plan holds. Antares has also been selected for a proposed deployment at Joint Base San Antonio under an Air Force initiative, while its reactor design and manufacturing work is concentrated at its Southern California headquarters.
Credence Research analysis
The NSDA itself is an early, procedural milestone, but the pace behind it is the signal. Antares took Mark-0 from design agreement to criticality in roughly eight months and is now reusing the same core, fuel and test bay for Mark-1. That design continuity reduces the number of new variables in the next safety review and suggests the company is building a repeatable authorization playbook rather than a one-off demonstration. Mark-1 is likely to face more scrutiny than Mark-0, however, because sustained power operation introduces thermal loads, fuel burnup and power conversion risks that a zero-power test never exercises.
The larger question is whether the federal pathway now taking shape, DOE authorization for testing, Army regulation for installations and a streamlined NRC route for commercial sales, can carry microreactors from prototypes to fleets. Janus pays on milestones, so schedule slippage translates directly into delayed revenue for every vendor. Developers that convert test data into regulatory credit fastest and secure scarce HALEU and TRISO supply early will be best positioned when civilian buyers such as data center operators and remote industrial sites start comparing offers.
What comes next
- DOE review of Mark-1 preliminary and final documented safety analyses, the next gates before fuel loading.
- Federal Register publication of the NRC rule on DOE- and DOD-authorized designs, which ANS reported was scheduled for Oct. 28, followed by a 30-day effective period.
- Full-power operation of Mark-1 at Idaho National Laboratory for several months in 2027.
- Disclosure of Mark-1's electrical output and Brayton cycle performance data.
- Initial deliveries to defense customers from 2028, including the first reactor at Fort Bragg under the Army's September 2028 target.
Sources
- Antares: Antares Clears First DOE Authorization Gate for Mark-1, Its Electricity-Producing Reactor (Business Wire)
- Antares: Company updates
- U.S. Army: Army reaches agreement with private industry for nuclear micro-reactors
- U.S. Department of Energy: Department of Energy Celebrates Fourth Criticality Ahead of July 4th Goal
Image: TRISO fuel research, by Oak Ridge National Laboratory via Wikimedia Commons, CC BY 2.0. Cropped and edited by Credence Research.
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About the Author
Senior News Editor at Credence Research Inc