DOE Announces First Advanced Reactor Criticality in U.S.

Antares Nuclear's Mark-0 advanced reactor design completed a zero-power fueled criticality demonstration at the Department of Energy's Idaho National Laboratory today under the DOE Reactor Pilot Program. U.S. Energy Secretary Chris Wright said, "For the first time in more than four decades, a new privately developed non-light-water reactor has reached criticality in the United States."

The achievement marks the first of multiple advanced reactors anticipated to go critical by the July 4th deadline set by President Trump in his May 2025 executive order. Assistant Secretary of Nuclear Energy Ted Garrish noted, "The skeptics didn't believe President Trump's Reactor Pilot Program could achieve criticality in less than a year. Today, we celebrate the first of the pilot projects to reach criticality."

Antares CEO Jordan Bramble said the demonstration will inform design and licensing for future commercial deployments, with microreactors expected to provide electricity from 2027 and beyond and to serve terrestrial, space and military-installation applications after further tests and licensure by the Nuclear Regulatory Commission.

The Reactor Pilot Program leverages DOE authorization to expeditiously certify and construct first-of-a-kind advanced reactor designs for demonstration. Building on this success, DOE recently established the Nuclear Energy Launch Pad to further accelerate advanced nuclear technologies. The Mark-0 is the 53rd reactor built at the Idaho National Laboratory site since 1951.