Radiant today announced that the U.S. Department of Energy (DOE) has granted approval of its Documented Safety Analysis (DSA). The approval marks a key milestone toward full-power testing of Radiant’s Kaleidos microreactor at Idaho National Laboratory (INL) and allows the company to advance to DOE’s Readiness Review, the next step before nuclear operations can begin.

Radiant’s scheduled testing at INL will be the industry’s only full-power, extended-duration demonstration of a nuclear microreactor to date. In addition to achieving criticality, Radiant will test the same Kaleidos unit for 60 effective full-power days (EFPD) over several months, demonstrating its performance under real operating conditions. The reactor being tested at INL uses a similar reactor design and custom-designed fuel as the units Radiant plans to deliver to customers, making the test a crucial step toward commercial deployment.

Radiant’s DSA approval addresses operation at power in addition to initial criticality, enabling the company to advance toward a more comprehensive evaluation of Kaleidos. Powered testing will allow Radiant to evaluate the reactor core, instrumentation, and integrated systems together under operating conditions.

“DOE’s approval is a major milestone because it reflects the scope of what we are preparing to demonstrate with Kaleidos,” said Dr. Rita Baranwal, Chief Nuclear Officer at Radiant. “We are testing the design of our commercial reactor, the same unit – from fueling through 150 hours of continuous operation without operator assistance and beyond. This approval for full-power demonstration is a first within the microreactor industry. It moves us forward to test our complete reactor system under sustained operating conditions.”

With the Kaleidos DSA approved, Radiant is queued for DOE’s Readiness Review, which will assess whether Kaleidos and the team responsible for operating it are prepared to begin nuclear operations. Following successful completion of the review, Radiant will fuel Kaleidos and begin its five-phase test campaign at the National Reactor Innovation Center’s Demonstration of Microreactor Experiments (DOME) facility at INL.

The campaign will progress from first criticality through increasingly higher-power operation, culminating in at least 150 hours of continuous operation at full-power without operator intervention.

The approval follows DOE’s February 2026 approval of Radiant’s earlier Preliminary Documented Safety Analysis (PDSA) submission.

“This milestone marks another important step forward in President Trump’s vision for an American nuclear renaissance,” said acting Deputy Assistant Secretary for Nuclear Reactors Chimi Zacot. “The Department of Energy is providing technical oversight to help companies like Radiant safely accelerate the development and testing of next-generation nuclear technologies, paving the way for faster commercial deployment of reliable, nuclear energy needed to power American industry, strengthen our national security and restore U.S. leadership in nuclear innovation.”

Radiant built Kaleidos at its El Segundo, California facility and shipped it to INL in August 2026. The DOME campaign is a key step toward Radiant’s plan to manufacture Kaleidos at its R-50 facility in Oak Ridge, Tennessee, and deliver its first commercial units to Buckley Space Force Base and Fort Benning in 2028. Earlier this month, Radiant was selected by the U.S. Navy to deploy Kaleidos at Naval Weapons Station Crane in Indiana.

About Radiant

Radiant is a leading developer of advanced nuclear technologies focused on delivering reliable, resilient, and scalable energy solutions that are transportable by land, sea and air. Radiant is committed to enabling a new generation of nuclear applications for commercial, industrial, and defense customers.

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