DOE Approves Radiant Kaleidos Microreactor Safety Plan
The Department of Energy cleared Radiant's safety analysis for its Kaleidos microreactor, a step that precedes any fuel loading or nuclear operations.
Updated on Nov. 2, 2026 in Nuclear
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The Department of Energy approved a safety analysis covering initial criticality and operation at power for Radiant's Kaleidos microreactor, which Radiant announced on Thursday, Oct. 29. Kaleidos must still pass a DOE Readiness Review before fuel loading and nuclear operations can begin.
Why it matters
The approval clears a regulatory checkpoint for a small advanced reactor design, but operations remain contingent on a further DOE review. The milestone is part of a broader push to test compact reactors before commercial deployment.
Radiant's test campaign at the DOME facility at Idaho National Laboratory calls for 60 effective full-power days and at least 150 hours of continuous full-power operation without operator intervention across five phases. The timeline for completing those phases and the results of the Readiness Review have not been announced.
The players
U.S. Department of Energy
The federal agency that oversees the nation's nuclear research programs and reviewed and approved the safety analyses for both reactor projects.
Radiant
A nuclear startup developing the Kaleidos microreactor, a small advanced reactor design.
Last Energy
A company developing small modular reactors, whose PWR-5 pilot received its own DOE safety approval on October 7.
The details
Radiant shipped Kaleidos to Idaho National Laboratory in August, and DOE approved its Preliminary Documented Safety Analysis in February 2026. The approved analysis covers initial criticality and operation at power, and testing will take place at the DOME test facility.
Timeline
February 2026: DOE approves Radiant's Preliminary Documented Safety Analysis.
August: Radiant ships Kaleidos to Idaho National Laboratory.
Oct. 7: DOE approves Last Energy's PWR-5 pilot safety analysis.
Thursday, Oct. 29: Radiant announces DOE approval of the Kaleidos safety analysis.
The Tech Race
The DOE's staged authorization model requires separate approval for each phase of testing, as shown by Last Energy's PWR-5 pilot, which is capped at 100 kilowatts thermal in its first phase. Radiant's Kaleidos campaign follows the same pattern, with its Readiness Review serving as the next gate before nuclear operations.
Compact microreactors like Kaleidos are designed as possible future power sources for remote sites and industrial users. Any commercial availability depends on whether DOME test results support later licensing applications, which the source describes only as a possibility.
The takeaway
Regulatory approvals for advanced reactors come in stages, and each stage is a checkpoint rather than a guarantee of operation. Readers following nuclear technology should track the Readiness Review as the next concrete signal.
What happens next
DOE must complete a Readiness Review before Kaleidos can load fuel and begin nuclear operations at Idaho National Laboratory.
Further reading
For background on the country's reactor testing programs, see Nuclear coverage on Wisevoter.
Source note: This article includes information reported by TokenPost.
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