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Radiant

Radiant

🇺🇸 El Segundo, US · Founded 2019 · Active

Radiant Industries, known as Radiant Nuclear, is a company in El Segundo, California, founded by a former SpaceX engineer, that is developing Kaleidos, a transportable microreactor it describes as 1 MW. Kaleidos is a high-temperature gas-cooled reactor using helium coolant and TRISO fuel, sized to fit in a shipping container, and designed to run for about five years before returning to the factory for refuelling. It is intended to replace diesel generators at military bases, hospitals and remote sites. The Department of Energy chose Radiant to be the first company to test at DOME, a microreactor test bed in the former EBR-II containment at Idaho National Laboratory, and its Kaleidos Development Unit was shipped there in August 2026. The US Air Force has selected Buckley Space Force Base for a Radiant reactor expected to operate in 2028.

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Sector
Fission
Technology
High-temperature gas-cooled reactor
Fuel
TRISO particle fuel, High-assay low-enriched uranium
Role
Reactor developer

Its recorded equity, $505m, is the 10th largest of the 25 organisations with a priced round here. Not every round is on record, so this is not its total raised.

Terms

High-temperature gas-cooled reactor
Helium-cooled and graphite-moderated, running far hotter than a water reactor. Fuel is TRISO particles, typically formed into pebbles or prismatic blocks, at LEU or HALEU enrichment depending on the design. The high outlet temperature suits industrial process heat as well as electricity.
TRISO particle fuel
Fuel kernels about the size of a poppy seed, each wrapped in layers of carbon and silicon carbide, so every particle acts as a tiny containment for its own fission products. The US Department of Energy reports that irradiated particles came through more than 300 hours of testing at temperatures up to 1,800 °C with no to minimal damage. That record covers the particle designs, temperatures and burnups actually tested; a claim outside that envelope is not covered by it.
High-assay low-enriched uranium
High-assay low-enriched uranium: uranium enriched to between 5% and just under 20% uranium-235, as the US Department of Energy defines it. It is still formally low-enriched, because the international line for highly enriched uranium is 20%, which is why many designs specify 19.75%. The binding supply constraint for many advanced reactor designs. The 5 to 10% part, which carries lighter US physical-security requirements than material from 10% up, is also tagged as LEU+. A developer calling fuel in that band 'LEU' is making a labelling choice, not describing a different enrichment.

Funding

$505m
equity in the 3 rounds recorded here
  1. 2025-12-17
    Equity round
    "More than $300 million" in a new round announced 17 December 2025, led by Draper Associates and Boost VC; the release gives no round name, so no round label is recorded. Lockheed Martin joined the round through Lockheed Martin Ventures (announced 17 February 2026, amount undisclosed). SEC Form D (filed 30 December 2025) reports $268,805,033 sold of a $350,000,018 offering at that date, below the $300 million headline, so the headline is recorded as a minimum and the Form D figure is kept here for comparison.
    $300m
  2. 2024-11-14
    Equity round · Series C
    Series C announced 14 November 2024 at $100 million, led by DCVC, and closed 28 May 2025 at $165 million with new investors including StepStone, Giant Ventures and ARK Venture Fund. One round: the $100 million first announcement is part of the $165 million, never a separate deal.
    $165m
  3. 2023-04-24
    Equity round · Series B
    Series B of $40 million announced 24 April 2023, led by Andreessen Horowitz. The release's "total capital raised to $54 million with an additional $2.3M in government awards" keeps the awards separate; neither total is a deal.
    $40m

Designs

Design Developer Approach Electrical output per unit Size class Licensing stage
Kaleidos Radiant High-temperature gas-cooled reactor Output not stated Not classed No milestone recorded

Related companies

Sources