Private Company
Appears in 2 stories
Fourth company in the pilot program to reach criticality
On June 4, 2026, Antares Nuclear's Mark-0 reactor at an Idaho desert lab started a self-sustaining nuclear reaction. It was the first privately built non-light-water reactor to do that in the U.S. in more than 40 years, and four rival startups matched the feat within nine weeks.
Updated Aug 8
Critical Test Reactor construction complete at INL; approaching criticality ahead of July 4 deadline
The Energy Department published its secretly rewritten nuclear safety rules on February 26, about a month after NPR first reported their existence. By early March, Aalo Atomics had completed its Critical Test Reactor at Idaho National Laboratory — assembled in 40 days, the first new reactor built at INL in 50 years — and said it would go critical within weeks.
Updated May 27
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