Radiant says its Kaleidos microreactor is now the only design in the world with U.S. government clearance to run at full power for months at a stretch. On October 29, 2026, the Department of Energy approved the Documented Safety Analysis, or DSA, for Radiant’s demonstration unit at Idaho National Laboratory, the final safety document DOE requires before a test reactor can operate at power on one of its own sites. Nobody has flipped a switch yet. What’s confirmed is a DOE approval and a test plan that, if it holds, ends with 60 days of full-power running spread across several months in 2027.
- DOE approved the DSA for Radiant’s Kaleidos Demonstration Unit (KDU) on Oct. 29, 2026, the company’s release says.
- The approval covers operation at full power, not just a first flicker of criticality.
- Next step is a DOE Readiness Review. No date has been published for it.
- The reactor sits at Idaho National Laboratory’s DOME test bed, run by DOE’s National Reactor Innovation Center.
- Kaleidos hasn’t generated electricity yet, and DOE authorization is not the same thing as an NRC license.
What the Radiant Kaleidos DOE Approval Actually Unlocks
A DSA sits near the top of a five-step ladder DOE built for its Reactor Pilot Program and Nuclear Energy Launch Pad, the same ladder we walked through when Antares’ Mark-1 cleared an earlier rung six days before Radiant did. Radiant’s own release says the approval “allows the company to advance to DOE’s Readiness Review, the next step before nuclear operations can begin.” DOE cleared Radiant’s Preliminary DSA back in February 2026, so this new approval is the fuller version of that safety case, covering the finished design rather than an early draft. Nobody has named a date for the Readiness Review, and nothing in this approval authorizes fuel loading or criticality on its own.
Three Companies, Three Reactors, One Busy October
Radiant wasn’t climbing this ladder alone last month. ANS Nuclear Newswire counted three Reactor Pilot Program companies clearing DOE milestones within a few weeks of each other:
| Company | Reactor | Latest DOE Milestone | Date |
|---|---|---|---|
| Antares Nuclear | Mark-1 | Nuclear Safety Design Agreement | Oct. 23, 2026 |
| Last Energy | PWR-5 | Documented Safety Analysis | Oct. 7, 2026 |
| Radiant | Kaleidos (KDU) | Documented Safety Analysis, full power | Oct. 29, 2026 |
Source: ANS Nuclear Newswire (Nov. 2, 2026) and company press releases.
Inside the Test Campaign at INL’s DOME
Once the Readiness Review clears, Radiant fuels the Kaleidos Demonstration Unit and starts what the company calls a five-phase test campaign. It begins at first criticality and climbs through progressively higher power levels. It’s meant to finish with at least 150 hours of continuous full-power operation, with no one touching the controls, something Radiant’s chief nuclear officer, Dr. Rita Baranwal, called “a first within the microreactor industry.” Radiant plans to keep testing that same unit for 60 effective full-power days, spread over several months. That’s the actual point of DOME, the National Reactor Innovation Center’s Demonstration of Microreactor Experiments test bed: proving a design holds up over weeks of real operation, not just a single moment of criticality.
The unit being tested isn’t a stand-in. Radiant’s release says Kaleidos uses “a similar reactor design and custom-designed fuel” to the units it plans to sell customers. Trade reporting puts the commercial design at roughly 1 megawatt-electric, helium-cooled, and built around TRISO fuel compact enough to ship in a single container. Radiant’s own release doesn’t publish those figures, which is worth flagging since a company usually leads with specs like that when it has them to share.
From El Segundo to Idaho Falls
Radiant built the tested unit at its factory in El Segundo, California, and shipped it to Idaho National Laboratory in August 2026, according to the company. We covered that move when it happened, months before this safety approval followed. Longer term, Radiant plans to manufacture Kaleidos units at a new factory it calls R-50, in Oak Ridge, Tennessee, a site with its own nuclear history stretching back to the Manhattan Project.
Where Kaleidos Goes After Idaho
DOME testing is step one, not the finish line. Radiant’s first commercial deliveries are planned for Buckley Space Force Base in Colorado and Fort Benning in Georgia, both targeted for 2028. A week before this safety approval, the U.S. Navy picked Kaleidos for Naval Weapons Station Crane in Indiana, a separate deployment from those Army and Air Force sites. None of those installations exist yet. Each one depends on DOME testing going as planned, the same bet every company in this program is making right now.
What’s Not Confirmed Yet
- “Only microreactor” is Radiant’s own framing, not an independent industry count. DOE separately cleared Last Energy’s PWR-5 pilot for its own DSA milestone earlier the same month.
- Radiant’s release gives no megawatt figure, fuel enrichment level, or container dimensions for Kaleidos. The 1 MWe, helium-cooled, TRISO-fueled specs come from trade reporting, not the company’s own announcement.
- No date has been published for the Readiness Review, or for when fueling and the first criticality test would actually happen.
- An INL presentation back in March 2026 had targeted fueling for May and criticality for June of this year. Neither happened on that schedule, so the new timeline carries the same risk.
- DOE authorization governs test reactors on DOE and military sites. It is not an NRC license, which a reactor selling power to the public grid would need instead.
Who Benefits and How
This is a defense and national-lab story first, so the payoff doesn’t reach an ordinary electric bill anytime soon. The clearest beneficiaries, if the DOME campaign goes as planned, are the military bases lined up to get a Kaleidos unit. Buckley Space Force Base, Fort Benning, and Naval Weapons Station Crane would each get a reactor built to keep running if the regional grid goes down, a resilience benefit for the service members stationed there rather than a bill-saving one for civilians. Around Idaho Falls, a multi-month test campaign means sustained lab work at INL, though Radiant hasn’t published a jobs figure tied specifically to this milestone.
The slower, wider benefit is the one every microreactor developer is chasing: proof that a factory-built reactor can run safely for weeks without a crew babysitting it. If DOME testing holds up, that’s the track record a future civilian customer, or a less defense-specific site, would eventually point to. None of that exists yet. It depends on a Readiness Review DOE hasn’t scheduled and a test campaign that hasn’t started.
Frequently Asked Questions
Is the Kaleidos reactor making electricity right now?
No. DOE approved the safety case that lets Radiant move toward operation. Fuel loading, criticality and power generation all still depend on a Readiness Review that hasn’t been scheduled.
Does the NRC regulate this reactor?
No. Kaleidos is moving through DOE’s own authorization process for test and demonstration reactors on DOE and military sites. A commercial Kaleidos sold to a non-federal customer would need separate authorization.
Which military bases will get a Kaleidos reactor?
Radiant’s release names Buckley Space Force Base in Colorado and Fort Benning in Georgia, both targeted for 2028. The Navy separately picked Kaleidos for Naval Weapons Station Crane in Indiana in October 2026.
Watch for the Readiness Review date once DOE sets one. That single calendar entry will say more than any press release about whether Kaleidos actually runs at full power on Radiant’s own schedule, or joins the long list of advanced reactor projects whose “next year” quietly became the year after.
Sources
- Radiant (Business Wire): Radiant Achieves Industry Milestone as the Only Microreactor Design to Secure DOE Safety Analysis Approval for Full Power Operations (press release, Oct. 29, 2026)
- Dealroom: DOE approves Radiant’s Kaleidos microreactor for full-power testing at Idaho National Laboratory (Oct. 29, 2026)
- ANS Nuclear Newswire: Antares, Last Energy, and Radiant hit DOE authorization milestones (Nov. 2, 2026)