Antares announced that its Mark-0 microreactor achieved initial criticality at Idaho National Laboratory under U.S. Department of Energy authorization. The reactor became the first private company to bring an advanced reactor to criticality under the DOE Reactor Pilot Program, marking a significant step for American nuclear energy development.

The demonstration involved partnerships with DOE, INL, BWXT, and the U.S. Army, with TRISO fuel fabricated by the Virginia-based company. Energy Secretary Chris Wright called it a historic moment for American nuclear energy, noting this represents the first non-light water privately developed reactor to reach criticality in over four decades.

Antares CEO Jordan Bramble emphasized the company met its ambitious timeline: criticality in 2026, electricity production in 2027, and military deployment by 2028. Engineers gained direct insight into core physics, control drum behavior, and supply chain maturity during the less than 12-month development cycle.

The achievement validates reactor physics parameters and supports the Army's microreactor deployment timeline for military installations. It establishes a replicable licensing pathway that could accelerate future reactor demonstrations on commercial timelines, moving from concept to criticality safely in under a year.