First Privately Built Advanced Reactor in Four Decades Goes Critical in Idaho

A privately developed nuclear reactor reached its first criticality, the point at which it sustains a controlled nuclear reaction, on June 4 at the Idaho National Laboratory, The Hindu reported. The United States Department of Energy described the milestone as a rebirth of the country's nuclear industry and a historic moment for American energy.

The reactor was built by Antares, a company founded in 2023 and backed by more than 140 million dollars in funding. Its Mark-0 microreactor became the first privately developed advanced reactor to reach criticality under the department's Reactor Pilot Program, according to the company. According to the company, it is the first new privately developed non-light-water reactor to reach criticality in the United States in more than four decades. Antares said it aims to produce electricity from an advanced reactor in 2027 and to begin deployments at United States military installations in 2028.

The achievement is part of a federal effort to accelerate advanced nuclear power, prompted by an executive order from President Donald Trump that set a deadline this summer for several reactors to reach criticality. The driver is demand. Artificial intelligence data centers are raising electricity consumption, and small modular reactors are being positioned as a steady, carbon-free source to meet it.