The US Department of Energy (DOE) has approved the nuclear safety design agreement (NSDA) for Antares Nuclear’s Mark-1, the company’s first electricity-producing nuclear power reactor.

The approval is the first step in the DOE’s authorisation process for Mark-1 and establishes the design requirements, safety analysis approach and regulatory expectations that will govern the reactor through construction and operation.

Mark-1 is scheduled to operate at full electrical power for several months in 2027 at Idaho National Laboratory. It uses the same full-scale core, Triso fuel, and test facility as Mark-0, which achieved criticality on 4 June 2026, as the first privately developed non-light-water reactor to do so in the US in more than four decades.