Antares Nuclear has achieved a significant milestone in U.S. energy innovation, successfully reaching zero-power criticality with its Mark-0 microreactor at Idaho National Laboratory. This marks the first time in more than four decades that a privately developed, non-light-water nuclear reactor has reached this stage in the United States. The demonstration underscores a resurgence in advanced nuclear technology and private-sector involvement in the nation's energy infrastructure.

The Mark-0 reactor benefited from collaboration with the U.S. Department of Energy and the U.S. Army, which is positioned as a future end user. It leveraged TRISO fuel developed under the Department of Defense’s Project Pele, fabricated by BWX Technologies in Virginia. The reactor was authorized under the DOE’s Reactor Pilot Program, which supports rapid deployment and regulatory coordination for next-generation nuclear systems.

Antares CEO Jordan Bramble highlighted the project’s unprecedented timeline, moving from concept to criticality in under 12 months. Idaho National Laboratory provided essential design, regulatory, and facilities support. Energy Secretary Chris Wright called the achievement a pivotal moment in the 'American nuclear renaissance,' aligning with a national goal set by President Trump to activate multiple advanced reactors by July 4, 2026.