Antares Nuclear Achieves Zero-Power Criticality for Mark-0 Reactor

• •Antares Nuclear's Mark-0 microreactor achieved zero-power criticality on June 4, 2026.
• •This milestone is the first for an advanced reactor at Idaho National Laboratory in over 50 years.
• •The reactor is part of the DOE's Reactor Pilot Program, which aims for commercial electricity production by 2027.

On June 4, 2026, Antares Nuclear's Mark-0 microreactor achieved zero-power criticality at Idaho National Laboratory, marking a significant milestone in the U.S. nuclear industry. This event, part of the DOE's Reactor Pilot Program, confirms the reactor's ability to sustain a fission chain reaction without generating electricity. Antares, founded in 2023, has raised over $140 million to develop this technology, which uses high-assay low-enriched uranium (HALEU) fuel. The Mark-0 is the first advanced reactor to achieve this milestone in over 50 years at INL and is expected to pave the way for future reactors to produce electricity by 2027. The achievement is seen as a key validation of Antares's reactor physics and control systems. Energy Secretary Chris Wright emphasized the importance of this event for America's nuclear renaissance, which aims to enhance energy security and reduce carbon emissions.