Nuclear Safety Design Agreement approval comes four months after Mark-0 criticality; Antares on track to generate electricity at Idaho National Laboratory in 2027
TORRANCE, Calif.--(BUSINESS WIRE)--Antares today announced that the U.S. Department of Energy (DOE) has approved the Nuclear Safety Design Agreement (NSDA) for Mark-1, the company's first electricity-producing reactor. The approval is the first step in DOE's authorization pathway 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 designed to operate at full electrical power for several months in 2027 at Idaho National Laboratory, integrated with Antares' nitrogen closed Brayton cycle power conversion system. It uses the same full-scale core, TRISO fuel, and test facility as Mark-0, which achieved criticality on June 4, 2026, as the first privately developed non-light-water reactor to do so in the United States in more than four decades.
The NSDA approval marks the second time in twelve months that Antares has initiated DOE's authorization process for a reactor. Mark-0 moved from NSDA approval in October 2025 to criticality in eight months, receiving DOE approval of its Preliminary Documented Safety Analysis and Documented Safety Analysis along the way. Mark-1 now follows the same sequence.
"Mark-0 proved we could take a reactor from a paper design to a self-sustaining chain reaction on the timeline we promised," said Jordan Bramble, CEO and Co-Founder of Antares. “Mark-1 isn’t a scaled-down, stand-in test rig. It’s commercially representative of the plant we’ll deploy to Fort Bragg under the Army Janus program in 2028. Mark-1 will be the first full-scale electricity-producing microreactor test in the United States. Operating at full electrical power for six months gives us comprehensive test data on every major subsystem and how they behave together. DOE’s approval of this safety agreement is the gate that lets us move not only from neutrons to electrons, but to customer plants, on schedule.”
Mark-1 is the bridge between demonstration and deployment. Data from its 2027 operating campaign will support Antares' initial deliveries to defense customers beginning in 2028, including the first of multiple reactors at Fort Bragg, North Carolina, under the U.S. Army's Janus program.
About Antares
Antares is a nuclear fission energy company developing compact microreactors for defense and space applications, delivering safe, reliable power where traditional energy sources cannot. Founded in 2023, Antares achieved initial criticality of its Mark-0 microreactor in 2026 under the DOE Reactor Pilot Program, and is on track to produce electricity in 2027, with initial production deployments to U.S. military installations beginning in 2028. Antares operates facilities in Torrance, California; Washington, D.C.; Idaho Falls, Idaho; and Aiken, South Carolina.
Contacts
Media contact:
Kayla Haas
kayla.haas@antaresindustries.com
