Radiant wins first-ever DOE approval for full-power microreactor, 1-megawatt Kaleidos cleared while every rival stopped at zero-power tests, Oklo and NuScale crash to multi-year lows

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The US Department of Energy has approved the safety analysis for Radiant's Kaleidos microreactor, the first clearance in the department's pilot program to cover operation at power rather than zero-power criticality tests. The 1-megawatt, truck-transportable reactor is sitting in the DOME test bed at Idaho National Laboratory awaiting fuel. Nuclear stocks, meanwhile, spent the same week falling to their lowest levels in years.

Radiant, based in Los Angeles, is the only entrant in the DOE pilot to have moved past zero-power testing. Antares, Valar Atomics, Deployable Energy and Aalo all reached criticality at Idaho ahead of a July 4 deadline, and Oklo's Groves test reactor followed in Texas on August 5 — every one of them a zero-power demonstration. Kaleidos now proceeds to a DOE Readiness Review, then to fueling and a five-phase campaign ending in at least 150 hours of continuous full-power operation with no operator intervention, followed by 60 effective full-power days on what Radiant says is essentially the design and fuel commercial customers will receive. The approval follows the department's February sign-off on Radiant's preliminary safety analysis.

Oklo closed Friday at $25.25, down 86 per cent from its October 2025 peak and at its lowest since April 2025. NuScale is down 89 per cent, trading at prices last seen in April 2024.

Radiant's order book shows who is actually buying. The company holds a binding agreement with the Army's Defense Innovation Unit worth up to $750 million for 15 units under the Janus program, was selected in April by the Air Force to develop and operate a microreactor at Buckley Space Force Base in Colorado, and was picked on October 20 by the Navy to deploy Kaleidos at Naval Weapons Station Crane in Indiana — the only nuclear company working with all three military branches. First commercial units are slated for Buckley and Fort Benning in 2028, and the data-center operator Equinix has signed for 20 units. The revival runs through the Pentagon first and private buyers second.

Production is assigned to a 300,000-square-foot campus in Oak Ridge, Tennessee, which will also handle fueling, refueling and spent-fuel storage so that customer sites never store spent fuel. Each unit runs up to five years between refuelings, needs no cooling water, and carries a 20-year design life.

The department's acting deputy assistant secretary for nuclear reactors, Chimi Zacot, called the approval "another important step forward in President Trump's vision for an American nuclear renaissance."