Antares Nuclear’s Mark-0 microreactor reached a key milestone at Idaho National Laboratory, proving a bold, faster path for advanced nuclear under the Department of Energy’s Reactor Pilot Program born from President Trump’s 2025 executive action. The privately developed, non-light-water reactor hit criticality on the schedule its team set, offering tangible evidence that industry and government can move quickly when given clear direction. This moment matters for energy strategy and national security as the program shifts from promises to measured results.
Antares announced that the Mark-0 achieved initial criticality under DOE authorization, marking the first time a private company has brought an advanced reactor to this point through the Reactor Pilot Program. That achievement puts a spotlight on a different model of nuclear development, one focused on rapid testing, iteration, and delivery instead of multiyear waiting games. The company is based in Torrance, California and has been pitching speed and practicality from the start.
Jordan Bramble, Antares CEO, underscored the company’s focus on delivering what it promises and keeping to a tight timeline. “Hitting our commitments is everything to us. Nuclear in America has been defined for too long by delays, by companies that said they would and then didn’t,” he said. “We said criticality in 2026, electricity production in 2027, and power to the warfighter in 2028. Today is the first of those commitments delivered on the schedule we set.”
Criticality is the moment a reactor sustains a self-perpetuating chain reaction, and it stands as the technical gate that unlocks further testing and deployment. Antares says the Mark-0 demonstration validated core reactor physics, supplied important testing data, and exercised control systems in real conditions. Those results will shape design tweaks and regulatory conversations down the road.
The Department of Energy confirmed the milestone and framed it as a milestone for American nuclear innovation. “Today’s achievement is a historic moment for American nuclear energy,” Energy Secretary Chris Wright said in a statement. “By bringing the first American non-light water privately developed reactor to criticality in more than four decades, Antares has shown what is possible when American innovation is unleashed.”
The milestone landed a bit over a year after President Trump signed a package of executive actions aimed at accelerating reactor testing, boosting domestic fuel production, and clearing pathways for advanced reactor technologies. Those decisions set aggressive expectations for the private and public teams working on next-generation designs. For conservatives who pushed for streamlined processes, the pilot program is beginning to deliver visible outcomes.
One specific directive, Executive Order 14301, instructed the Department of Energy to stand up a pilot program to speed testing of advanced reactors with a public target date for criticality. Bramble noted the team met that deadline. “The President and DOE set an ambitious timeline for reactor testing, and we met that challenge,” Bramble said.
The test was a collaborative effort involving Idaho National Laboratory, DOE, and BWX Technologies, with the U.S. Army listed as a planned end user for deployable power. The Mark-0 used TRISO fuel fabricated by BWXT and drew on fuel work done through Project Pele, the Defense Department’s initiative for transportable microreactors. That mix of private engineering, lab expertise, and military interest frames this as both a commercial and strategic achievement.
“The skeptics didn’t believe President Trump’s Reactor Pilot Program could achieve criticality in less than a year,” Assistant Secretary of Nuclear Energy Ted Garrish said. “Today, we celebrate the first of the pilot projects to reach criticality and the people who rolled up their sleeves to shape the future of nuclear energy in the United States.”
Engineers reported they gained immediate, actionable insight into reactor physics behavior, control systems and the supply chain under test conditions. That hands-on data matters for licensing and for accelerating subsequent designs toward commercialization. “We went from concept to a critical reactor, safely, in less than 12 months. That doesn’t happen by accident. The team treated the schedule as non-negotiable,” Bramble said.
Antares plans to begin producing electricity at the same Idaho facility in 2027 and remains on track to deliver electricity-generating microreactors to U.S. military sites by 2028. Those targets keep pressure on the program to move from demonstration to durable capability. If the timelines hold, the result could be a new, faster rhythm for American nuclear innovation and a practical boost for military energy resilience.
