6 Nuclear SMR Startups Powering the AI Datacenter Boom
AI datacenters are drinking the grid dry. These 6 nuclear SMR startups are raising billions to deliver the clean, firm power Big Tech can't live without.
Key Takeaways
- Grid crisis is real: Google's 2026 Environmental Report shows a 37% surge in electricity demand from AI, forcing hyperscalers to bet on nuclear as the only firm clean power source.
- $4.5 billion year: Global VC funding for nuclear fission and fusion startups topped $4.5 billion across 81 companies in 2026 alone, a 3x acceleration from 2024.
- Proof exists: On July 1, 2026, Valar Atomics became the first advanced nuclear startup to directly power AI hardware, running an Nvidia DGX Spark from its Ward 250 reactor.
- Deals are binding: Meta secured 6.6 GW of nuclear capacity from three partners; Amazon backed 5 GW from X-energy alone. Signed contracts, not letters of intent.
- Factory wins: SMR startups using modular, factory-made reactor designs are compressing build timelines from 15 years to under 5.
On July 1, 2026, a team member at a remote Utah site plugged an Nvidia DGX Spark into an outlet. Nothing unusual, except the outlet was fed by electricity from the Ward 250, an advanced nuclear reactor that had achieved its first self-sustaining chain reaction just two weeks earlier. The startup behind it, Valar Atomics, was founded in 2023 by a 27-year-old high school dropout. It was the first time an advanced nuclear reactor directly powered AI hardware.
That moment crystallized what the venture world has been building toward for three years. AI's insatiable power hunger has turned nuclear from a politically toxic topic into the most bankable infrastructure bet in Silicon Valley. Since 2024, every major US hyperscaler, Microsoft, Google, Amazon, and Meta, has signed at least one nuclear power deal. According to investment tracking from 2026, 13 announced projects have committed over 9.8 GW of nuclear capacity to AI datacenter infrastructure alone.
Why Big Tech Went Nuclear
The problem is simple. In its 2026 Environmental Report, Google disclosed a 37% surge in electricity demand, the largest single-year increase in the company's history, driven almost entirely by AI infrastructure. Solar and wind can not solve this alone: AI training clusters require firm power on demand, 24 hours a day, regardless of cloud cover or wind speed. Natural gas creates regulatory and ESG risk. Nuclear is the only low-carbon, always-on power source that can scale to gigawatts.
The hyperscaler deals reflect this urgency. Meta announced agreements to secure up to 6.6 GW of nuclear capacity. Amazon backed five gigawatts of new Small Modular Reactor (SMR) projects with X-energy. Google signed the world's first corporate SMR purchase agreement, committing to 500 MW from Kairos Power.
For investors tracking the AI infrastructure buildout, nuclear is no longer a 10-year moonshot. It's a 5-year commercial reality. The question is which startups have the regulatory clearance, manufacturing scale, and signed offtake to actually deliver on that timeline.
Kairos PowerFluoride salt-cooled reactors for firm power
Kairos Power made history in October 2024 when it signed the first corporate SMR purchase agreement in US history with Google, committing to 500 MW across six to seven reactors by 2035. The first unit is targeted for 2030.
Founded in 2016 by nuclear engineers Edward Blandford, Per Peterson, and Mike Laufer, Kairos builds fluoride salt-cooled high-temperature reactors. The design uses molten salt as a coolant with TRISO ceramic pebble fuel, running at low pressure and eliminating the pressurized-vessel failure modes of conventional light-water reactors. The Hermes demonstration reactor in Oak Ridge, Tennessee is under construction with NRC permit in hand.
Why watch it now: A power purchase agreement with the Tennessee Valley Authority formalized the Google deal into a binding utility framework in August 2025. Kairos now has both the fuel supply chain and the construction mandate locked in. The Hermes demo reactor could begin operating in 2027, and its learnings will directly feed into the commercial fleet Google is purchasing.
X-energyXe-100 gas reactor with integrated fuel production
When Amazon invested in October 2024, it did not just write a check. It backed five gigawatts of new SMR projects, signaling industrial-scale ambition. X-energy closed a $700 million upsized Series C-1 round in February 2025, anchored by Amazon's Climate Pledge Fund with participation from Jane Street, Ares Management, and Emerson Collective, bringing total capital raised to over $1.4 billion.
Dr. Kam Ghaffarian founded X-energy to commercialize high-temperature gas-cooled reactor technology. The Xe-100 is an 80 MWe pebble-bed reactor operating at temperatures high enough to produce industrial hydrogen and process heat, not just grid electricity. X-energy also manufactures its own TRISO-X fuel, giving it a vertically integrated supply chain most competitors lack.
Why watch it now: X-energy filed for a public market listing in 2026. The combination of Amazon's 5 GW commitment, a proprietary fuel business, and dual-use industrial applications (power plus hydrogen) gives it more addressable revenue than any other SMR startup on this list.
TerraPowerNatrium sodium-cooled reactor with molten salt storage
TerraPower is the most capital-heavy and most construction-advanced player on this list. Founded in 2006 by Bill Gates alongside Nathan Myhrvold and Dr. John Gilleland, it has raised over $1.4 billion in total, including a $650 million round from Gates, NVIDIA Ventures, and HD Hyundai. CEO Chris Levesque, who joined in 2015, leads day-to-day operations.
The Natrium reactor delivers 345 MW using a sodium-cooled fast reactor with integrated molten salt energy storage, allowing it to surge output during peak demand without spinning up additional generation capacity. The first Natrium plant is under construction in Kemmerer, Wyoming. In March 2026, the Nuclear Regulatory Commission unanimously approved the construction permit.
Why watch it now: Meta signed contracts for up to eight Natrium plants totaling up to 2.76 GW of firm capacity to power its Prometheus AI supercluster in Ohio. TerraPower is the only company on this list with a reactor under active construction, NRC sign-off, a signed hyperscaler deal, and Nvidia money on the cap table simultaneously.
Last EnergyNuclear-as-a-service via 20 MW modular plants
Last Energy inverts the traditional nuclear business model. Rather than selling reactors or building for a utility, it acts as designer, owner, and operator, delivering power via long-term power purchase agreements. Think of it as nuclear infrastructure as a service.
Bret Kugelmass founded Last Energy in 2019 as a commercial spinoff of the Energy Impact Center. The PWR-20 is a 20 MW pressurized water reactor engineered for speed: each plant is designed to be manufactured, transported, and assembled within 24 months of contract signature. Last Energy raised $100 million in Series C funding in December 2025, led by the Astera Institute, with Galaxy Fund, Gigafund, and Woori Technology participating. The company has signed agreements for 51 units across Europe, representing an estimated $32 billion in contracted value.
Why watch it now: Last Energy's 20 MW modular plants are sized to co-locate with a single large datacenter, simplifying the customer procurement process versus buying into a utility-scale 345 MW plant. The European pipeline represents committed revenue that most US-focused peers do not yet have.
If you are systematically tracking startups like these across the energy and AI infrastructure space, cross-referencing them against the Unicorn Screener leaderboard is a fast way to surface which companies are scoring highest on traction, team, and market timing. Unicorn Screener evaluates startups against the same dimensions institutional investors prioritize.
Radiant NuclearPortable 1 MW microreactors for datacenters
Radiant is thinking smaller than everyone else: 1 MW at a time, delivered via semi-truck. Founded in 2020 by ex-SpaceX engineers Doug Bernauer (CEO) and Bob Urberger (CTO), Radiant's Kaleidos microreactor uses helium cooling and TRISO fuel, enough for five years between refueling cycles with no on-site diesel exhaust.
In December 2025, Radiant closed a $300 million Series D led by Draper Associates and Boost VC at a $1.8 billion valuation. Earlier investors include Andreessen Horowitz, DCVC, and Union Square Ventures. The company signed a deal with Equinix, the global datacenter operator, to supply 20 Kaleidos reactors, making Equinix its first major named datacenter customer. Radiant's mass-production factory in Oak Ridge, Tennessee breaks ground in 2026 alongside a demonstration unit test at the DOE's DOME facility.
Why watch it now: Radiant is building to Amazon's distributed infrastructure playbook. Twenty reactors at a single data center operator create recurring revenue, a repeatable supply chain, and a referenceable customer. That is a commercial flywheel no utility-scale competitor can replicate at the same speed.
Valar AtomicsFactory-made high-temp gas reactors for AI
The youngest company on this list just pulled off the most dramatic milestone in the sector. On July 1, 2026, Isaiah Taylor, the 27-year-old founder and CEO of Valar Atomics, demonstrated electricity from his Ward 250 reactor running an Nvidia DGX Spark AI computer at the company's Orangeville, Utah test site. It was the first time an advanced nuclear reactor directly powered AI hardware in a live demonstration.
Taylor founded Valar Atomics in 2023, naming the reactor line after his great-grandfather Ward Schaap, a Manhattan Project physicist. The Ward 250 is a 5 MW high-temperature gas-cooled reactor using TRISO fuel and helium coolant, a design proven through decades of German and US research. On August 3, 2026, just eight days before this article's publication, Sequoia Capital partner Shaun Maguire led a $1 billion Series B at a $6 billion valuation, with earlier backers including Palmer Luckey and Palantir's Shyam Sankar.
Why watch it now: Valar is the only company on this list that has already generated electricity from an advanced nuclear reactor and used it to run AI hardware. Every other company here is in regulatory review or early construction. Valar has a running reactor. That distinction is not minor, it's the difference between a plan and proof.
How the Six Compare
| Company | Reactor Type | Capacity | Key Partner | Stage |
|---|---|---|---|---|
| Kairos Power | Fluoride salt-cooled | ~140 MW/unit | Google (500 MW PPA) | Demo under construction |
| X-energy | High-temp gas pebble bed | 80 MW/unit | Amazon (5 GW commitment) | Pre-commercial |
| TerraPower | Sodium-cooled fast reactor | 345 MW | Meta (2.76 GW signed) | Construction started |
| Last Energy | Pressurized water | 20 MW | 51 European units signed | Permitting |
| Radiant Nuclear | Helium-cooled micro | 1 MW | Equinix (20 units signed) | Factory production 2026 |
| Valar Atomics | High-temp gas | 5 MW | Nvidia (demonstrated) | Running reactor |
One pattern stands out across the most fundable energy startups of the past year: the winners sign a named customer offtake agreement before the reactor is running. Every company above has at least one. That is not coincidence.
What This Means If You're Investing
The AI power crisis and the US energy independence push arrived simultaneously. That combination is producing a level of corporate nuclear investment not seen since the 1970s, except this time the off-takers are not regional utilities. They are Microsoft, Google, Amazon, and Meta, companies with the balance sheets to co-fund construction before a single watt is delivered.
The SMR startups on this list have compressed the traditional 20-year nuclear timeline to 5 to 7 years by using factory production, front-loading offtake agreements, and running regulatory tracks in parallel. The technical risk is still real. But the market risk is lower than it has ever been for nuclear energy. No model can guarantee which reactor design emerges as the dominant standard. What is certain is that the grid simply cannot keep up with AI demand on solar and gas alone, and every smart dollar in the sector already knows it.
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