An advanced reactor developed under a Department of Energy pilot program reached a key milestone.

Antares Nuclear's Mark-0 microreactor reached initial criticality under DOE authorization, the company announced. Criticality is the point when a reactor achieves a self-sustaining nuclear reaction. 

This makes Antares the first private company to reach the milestone under the DOE's Reactor Pilot Program. The program was established by Trump's 2025 executive order, directing the acceleration of America's advanced nuclear reactors. 

Antares said that the demonstration of criticality validated key reactor physics parameters and provided data to help future reactor development. 

"By bringing the first American non-light water privately developed reactor to criticality in more than four decades, Antares has shown what is possible when American innovation is unleashed. The Trump administration is proud to support the rebirth of America’s nuclear industry and ensuring Americans have access to affordable, reliable and secure energy for generations to come," Energy Secretary Chris Wright said in a statement.