Antares Receives DOE Preliminary Document Safety Approval for Mark-0 Demonstration Reactor

Safety milestone puts Antares months away from its first nuclear reactor demonstration at Idaho National Laboratory

IDAHO FALLS, Idaho--(BUSINESS WIRE)--Antares, a nuclear fission energy company developing microreactors for defense and space applications, today announced that the U.S. Department of Energy (DOE) has approved the company's Preliminary Documented Safety Analysis (PDSA) for its Mark-0 reactor, Antares' first demonstration reactor, scheduled to achieve criticality before July 4, 2026 under DOE’s Reactor Pilot Program.

The PDSA is an important milestone. With this approval, the DOE is certifying that Antares’ reactor, facility, and planned operations meet the standards and expectations of the Department. This approval validates the company's safety case and establishes a clear pathway to final DOE authorization as Antares prepares for fabrication, assembly, installation, and operation.

Antares is one of a select group of companies participating in the DOE's Reactor Pilot Program, which enables advanced reactor demonstrations at national laboratories. The Antares Mark-0 will be among the first reactors to reach criticality, or achieve a controlled, self-sustaining fission reaction, under the program.

"The DOE approval of our PDSA is an important step on our way to criticality and ultimately producing power for defense and space applications. Safety is at the core of everything we do, and we thank the DOE for their continued partnership," said Jordan Bramble, CEO of Antares. “We are excited to turn on our low-power demonstration unit before July 4, and we look forward to learning valuable lessons on fueling, reactor controls, and the physics of our core from our Mark-0 operations.”

Antares will test Mark-0 at Idaho National Laboratory (INL) in Building 793 of the Materials and Fuels Complex. The Antares Mark-0 will use a full-scale core. The same facility and fuel used in Mark-0 will support Antares' electricity-producing demonstration in 2027. Decades ago, this same building housed ML-1, the U.S. Army's first mobile nuclear reactor. Since 2024, Antares has worked to establish this facility as an enduring testbed, enabling rapid progress without the need for groundbreaking construction. The company has invested over $40 million in Idaho and maintains a growing presence in Idaho Falls.

"We're grateful for our partners at DOE and INL, and for congressional leaders and senior officials at the Pentagon who continue to support the American nuclear renaissance," Bramble said.

Antares has secured an allocation of High-Assay Low-Enriched Uranium (HALEU) fuel feedstock from DOE, with fuel fabrication currently underway in collaboration with BWX Technologies. The company has raised over $130 million in funding to date, including a $96 million Series B round announced in December 2025, and holds more than $13 million in active government contracts, including with the Pentagon and NASA.

About Antares
Antares is building compact nuclear microreactors to deliver reliable, rapidly deployable energy where it’s needed most: remote military bases, austere industrial sites, and, one day, deep space and underwater missions.