The U.S. Department of Energy has approved the Nuclear Safety Design Agreement (NSDA) for Antares's Mark-1 reactor, the company announced on 23 October. The agreement is the first step in DOE's authorisation pathway, establishing design requirements, the safety analysis approach and the regulatory expectations for construction and operation.

Six months at full power

Mark-1 is described as the first full-scale electricity-producing microreactor test in the United States, targeted to run at full electrical power for six months. That is a materially different proposition from a zero-power criticality demonstration: it requires sustained fuel performance, heat rejection and grid-interface behaviour over a long operating campaign.

Mark-0 already on the board

Antares's Mark-0 was the first reactor to achieve criticality by the 4 July deadline set by U.S. President Donald Trump, completing a zero-power fuelled criticality demonstration at Idaho National Laboratory in June using BWXT-supplied fuel. The company has also been selected by the U.S. Army for deployment at Fort Bragg, North Carolina, under the Janus Program, following a May 2025 executive order calling for an Army-regulated reactor at a domestic military installation.

The HALEU behind the hardware

Every one of those milestones depends on enriched fuel. Antares has signed a HALEU contract this year with U.S. enricher Centrus, as well as a contract with European-headquartered Urenco for HALEU to be produced at the company's facility currently under construction at Capenhurst in the UK. On the fabrication side, it holds TRISO agreements with BWXT Advanced Fuels — an initial tonne, fabricated at Lynchburg, Virginia — and with Standard Nuclear, for a minimum of one tonne and up to eight tonnes through 2035.

Two qualified fuel sources plus two HALEU suppliers is a deliberately redundant chain for a company whose reactors are small enough to be transported by road.

The pattern is becoming familiar across the advanced reactor sector: the developers moving fastest are the ones contracting enrichment and fabrication years before first power, rather than treating fuel as a procurement detail to be resolved during construction.

This article was assisted by AI analysis. Please refer to the original source for official information.