DOE approves Radiant's Kaleidos microreactor for full-power testing at Idaho National Laboratory
What's the deal? Radiant, the El Segundo, California-based developer of portable nuclear microreactors, said on 29 October that the US Department of Energy has approved the Documented Safety Analysis for its Kaleidos reactor. It is the final safety document a reactor needs before it can operate in a DOE facility, and it covers running at power, not just reaching first criticality.
The reactor: Kaleidos is a helium-cooled, high-temperature gas reactor running on TRISO fuel, rated at about 1 MW of electricity (3 MW thermal) and sized to fit in a single shipping container, according to Nuclear News Network. Radiant built the unit in El Segundo and shipped it to Idaho National LaboratoryDealroom has a profile for this one. Try Dealroom → in August.
What's next? A DOE Readiness Review, which checks whether the reactor and the team that will run it are ready for nuclear operations. If it passes, Radiant will load fuel and start a five-phase test campaign at the National Reactor Innovation Center's DOME test bed, building from first criticality to at least 150 hours of continuous full-power operation without operator intervention, and 60 effective full-power days over several months. "This approval for full power demonstration is a first within the microreactor industry," said Rita Baranwal, Radiant's chief nuclear officer. No date has been published for the review.
The caveats: The "only microreactor" claim is Radiant's own; DOE also approved a safety analysis for Last Energy's PWR-5 pilot reactor at Texas A&M-RELLIS in October through a separate programme, Nuclear News Network notes. A DOE test authorisation is not a Nuclear Regulatory Commission licence, which commercial units will still need. And the schedule has slipped: an INL presentation from March targeted fuelling in May and criticality in June 2026.
What's the endgame? Radiant plans to manufacture Kaleidos at its R-50 factory in Oak Ridge, Tennessee, and deliver its first commercial units to Buckley Space Force Base and Fort Benning in 2028. Earlier in October the US Navy selected it to deploy Kaleidos at Naval Weapons Station Crane in Indiana.
The signal: Microreactors have been promised for years; a full-power, multi-month test of a factory-built unit would be the first real operating data for the category. The milestone drew wide attention on X, where a post calling it a first "in American history" passed 950,000 views.
Read more: Radiant, Business Wire, Nuclear News Network, Interesting Engineering, Neutron Bytes, Atoms Not Bits (X)
Image credit: Radiant
