The archive · Climate & Energy · Product decision · 2020–2026
Radiant's portable-reactor bet: $300M at $1.8B, first full-power test approved for INL
Radiant raises $300M+ to put a 1MW helium-cooled microreactor on a semi-truck; DOE approves the first full-power test, set for summer 2026 in Idaho.
Radiant
What the business is
Radiant builds Kaleidos, a 1-megawatt helium-cooled microreactor that fits on a semi-trailer, with TRISO fuel lasting five years, aimed at commercial and military sites.
Starting capital：$300M+ round led by Draper Associates and Boost VC (Dec 2025) at a valuation above $1.8B; $165M raised six months earlier in May 2025
How it started
Founded in 2020, Radiant set out to replace diesel generators at remote commercial and military sites with a reactor small enough to deliver by truck. The Kaleidos design uses helium cooling and TRISO fuel — carbon- and ceramic-coated uranium beads designed to resist meltdowns — and the company positioned the reactor as a replaceable product rather than a plant project.
What happened
Radiant raised $165M in May 2025, signed a deal with Equinix in August 2025 to supply 20 reactors, and closed a $300M+ round in December 2025 led by Draper Associates and Boost VC with participation from Chevron Technology Ventures and Founders Fund, valuing the company above $1.8B. It was also one of 11 companies selected for a federal program targeting three reactors reaching criticality by July 4, 2026. On February 9, 2026, the DOE granted approval of Radiant's DOE Authorization Request for Kaleidos — described as the first approval granted for a full-power test — keeping the company on track to start its first reactor in summer 2026 at the NRIC's DOME facility at Idaho National Laboratory.
How it ended up
Still running: the full-scale test campaign at INL is approved and on schedule for summer 2026 startup, with initial customer deployments targeted for 2028; no reactor has yet been started.
Background
Radiant is a nuclear startup founded in 2020 to build Kaleidos, a 1-megawatt helium-cooled microreactor that fits on a semi-trailer. The reactor is designed to run five years on TRISO fuel — carbon- and ceramic-coated beads of graphite and uranium — and then be hauled away at the end of a 20-year lifetime, positioning the company as a seller of portable power rather than a builder of nuclear plants.
The bet is that microreactors can replace diesel generators and battery backup at commercial, data-center and military sites, where reliability and carbon-free operation matter more than scale. Customers can buy units outright or subscribe through a power-purchase agreement. Radiant also targeted data centers early, signing an agreement with Equinix in August 2025 to supply 20 reactors.
The company raised $165M in May 2025 and $300M+ in December 2025 — led by Draper Associates and Boost VC, with Chevron Technology Ventures and Founders Fund participating — at a valuation above $1.8B. It was one of 11 companies picked for a federal program aiming for three reactors at criticality by July 4, 2026. On February 9, 2026, the DOE approved Radiant's DOE Authorization Request for Kaleidos, the first approval granted for a full-power test, clearing the way for startup at the DOME facility at Idaho National Laboratory in summer 2026.
As of September 2026 the full-scale test campaign is approved and under preparation, with initial customer deployments targeted for 2028. The company's product thesis — mass-manufactured, transportable reactors with a service-like business model — now rests on the INL demonstration actually running.
What has to be true
- Replaces the megaproject model with a manufactured product: one reactor, one truck, five years of fuel, a 20-year life, then removal.
- Targets buyers who already pay premium prices for diesel and backup power at remote sites, where 1 MW of clean, continuous power is valuable.
- Sells two ways — outright purchase or power-purchase agreement — matching how data centers and military sites already buy power.
- Pursued the DOE authorization pathway deliberately, turning the first-ever full-power test approval into a regulatory template it can reuse for every unit.
What can be applied
A portable, productized reactor can raise nine-figure rounds before first criticality — but the thesis hinges on the INL test running and regulators accepting a repeatable full-power-test pathway.
Aftermath
As of 2026-09-02, Radiant's Kaleidos is in the full-scale test campaign at Idaho National Laboratory's DOME facility, with startup targeted for summer 2026 after DOE approval of its Authorization Request in February 2026. The company holds a 20-reactor supply agreement with Equinix, has raised over $300M at a valuation above $1.8B, and targets initial customer deployments in 2028. No reactor has yet been started, so the portable-power thesis remains unproven at the moment of first criticality.
Sources
- Radiant Nuclear raises $300M for its semi-sized 1 MW reactor
- Radiant Receives DOE Approval of Preliminary Documented Safety Analysis, Latest Milestone Towards Start-up of First Reactor
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