Antares Nuclear Reactor Reaches Criticality, Achieves Major Energy Milestone

This is the first time in more than 40 years that a new, privately developed non-light-water reactor has hit criticality in the United States.

The Department of Energy building in Washington on Nov. 17, 2025. Madalina Kilroy/The Epoch Times

Los Angeles-based Antares Nuclear’s advanced microreactor design, Mark-0, has achieved criticality, signifying the resurgence of the U.S. nuclear industry, the Department of Energy (DOE) said in a June 4 statement.

For a nuclear reactor, criticality means that it has achieved a perfectly stable state. Under such conditions, nuclear power plants can generate electricity around the clock.