Radiant is building the first mass-produced nuclear microreactor. Founded in 2020 by Doug Bernauer, a former SpaceX engineer who worked on Mars power systems, the El Segundo company makes Kaleidos — a 1 MW, helium-cooled, TRISO-fueled microreactor that ships on a semi truck, runs five years between refuelings, and is designed to replace diesel generators at military bases, data centers, remote sites, and disaster zones.
The momentum through 2025–26 has been unusual for a nuclear company. Radiant closed a $300 million+ Series D in December 2025 at a valuation above $1.8 billion — just six months after its $165 million Series C — then extended the round to a reported $350 million in January 2026 and added Lockheed Martin Ventures as a strategic investor in February. Its commercial and regulatory milestones stack up: first reactor design selected to test at Idaho National Laboratory’s new DOME facility, DOE safety-analysis approval received in February 2026, a deal with data-center operator Equinix for 20 reactors, an Air Force selection to deliver microreactors to Buckley Space Force Base, and a second DOE HALEU fuel allocation in July 2026 supporting a first commercial unit at a U.S. military installation. Customer deployments are targeted for 2028, with an R-50 factory breaking ground in Oak Ridge, Tennessee.
Can you buy Radiant stock?
Not on any exchange — Radiant is private, with no ticker. Accredited investors get exposure through:
- Direct secondary purchases — buying outstanding shares from an existing shareholder, subject to company transfer restrictions and rights of first refusal.
- Special purpose vehicles (SPVs) — pooled vehicles holding Radiant shares at smaller minimums than a direct block requires.
There is no meaningful public-proxy route — the cap table is venture funds (Founders Fund, a16z, Union Square Ventures, DCVC, Draper, Boost VC) and strategics like Lockheed Martin Ventures.
The Series D and where the valuation stands
At $1.8 billion+, Radiant is priced as the credible leader in a category — portable microreactors — that barely existed as an investable thesis three years ago. The re-rating logic: U.S. policy swung hard pro-nuclear in 2025–26 (streamlined NRC, executive orders accelerating test reactors), AI data-center power demand created an urgent commercial buyer class, and Radiant kept hitting milestones on schedule while peers slipped.
What to keep in mind before extrapolating:
- Radiant is pre-revenue in the sense that matters: no commercial reactor has yet operated. The first Kaleidos test at INL and the path from demonstration to 2028 deployments carry genuine technical and regulatory risk.
- Nuclear timelines slip more often than they hold. A one-year delay wouldn’t be surprising in this industry; a valuation built on schedule-keeping is exposed to it.
- Fuel supply (HALEU) is a sector-wide bottleneck; Radiant’s DOE allocations help, but the supply chain is young.
How access actually works
Radiant secondaries trade through brokers and SPV syndicators, typically with minimums from $100,000 upward. Because the company is private, expect:
- Transfer restrictions. Radiant can block or delay transfers; many trades settle through existing SPVs.
- Thin supply. The company is young, the round is fresh and was oversubscribed, and most holders are early funds with no urgency to sell.
- Milestone-driven pricing. Each INL and DOE milestone moves secondary asks; expect pricing to gap around test results rather than drift smoothly.
At the time of writing, we have visibility into live Radiant secondary supply, including allocations accepting indications from accredited investors. Terms, pricing, and structure are available on request to qualified investors.
Is Radiant worth the risk?
The bull case: category leadership in portable nuclear, an oversubscribed round with Lockheed Martin as a strategic, real government commitments (Air Force, DOE fuel allocations), a signed commercial anchor in Equinix, and a policy environment more favorable to new reactors than any in fifty years. The bear case: no operating commercial reactor yet, nuclear’s long history of schedule and cost overruns, fuel-supply dependency, competition from Oklo, Aalo, Antares, and others chasing the same data-center and defense demand, and the standard private-market risks — illiquidity, limited information, and a likely long hold before any exit.
This is a concentrated, illiquid position sized for the portion of a portfolio that can go to zero — true of every pre-IPO position, and especially of pre-revenue deep tech.