The US Department of Energy approved the Nuclear Safety Design Agreement (NSDA) for Antares' Mark-1 reactor on 23 October 2026 — the first gate in DOE's authorisation pathway for reactors tested under DOE authority at national laboratories. The NSDA sets design requirements, the safety analysis approach and the regulatory expectations governing construction and operation.
Second NSDA in twelve months
It is the second NSDA Antares has received in 12 months. Mark-0, the company's demonstration reactor, moved from NSDA approval in October 2025 to zero-power criticality on 4 June 2026, roughly an eight-month path. Mark-1 reuses Mark-0's full-scale core, TRISO fuel and test facility, pairing the reactor with a nitrogen closed Brayton cycle power conversion system. It is scheduled to run at full electrical output for several months in 2027 at Idaho National Laboratory.
The fuel supply chain behind the reactor
Mark-1's schedule depends on fuel arriving. Antares has assembled a multi-supplier HALEU portfolio, with supply agreements signed with Urenco in May 2026, General Matter in July 2026 and Centrus in September 2026 — covering its most constrained input with three separate enrichment sources. For TRISO fuel, used in both Mark-0 and Mark-1, Antares holds a multi-year supply agreement with Standard Nuclear announced in August 2026. The company raised a $470 million Series C round in July 2026 supporting the programme, including these fuel arrangements.
Demonstrated momentum under DOE's pilot programme
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 4 July 2026. DOE reported in July 2026 that Valar Atomics, Deployable Energy and Aalo Atomics also reached criticality, exceeding the target. Mark-0 operated at Idaho National Laboratory's Materials and Fuels Complex.
Demand signal from the military
In August 2026, the US 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.
Each of those designs implies demand for HALEU or TRISO fuel, tightening the link between microreactor deployment and enrichment capacity.
This article was assisted by AI analysis. Please refer to the original source for official information.