As of June 4, 2026, Antares Nuclear’s Mark-0 reactor became the first reactor in the Department of Energy’s Reactor Pilot Program to reach criticality at the Idaho National Laboratory. Antares is one of 11 companies taking part in the Pilot Program.
These reactors are not gigawatt-scale commercial plants, but they are essential first-of-a-kind demonstrations. Done well, the program can generate the data, operating experience, and regulatory lessons that help clear the path for commercial advanced reactor deployment. It fills the gap in the prototyping stage of the innovation cycle—a stage that is crucial for the U.S. to succeed. That Antares has been able to reach criticality a full month before the July 4, 2026 deadline established for the program is a welcome indicator of the program’s potential success.
