In recent years, the surge in artificial intelligence has driven electricity demand in the U.S. to unprecedented heights after decades of stagnation. This surge has prompted major technology companies to secure reliable power sources for their sprawling data centers.
Many are turning to nuclear fission—a power source that is experiencing a renaissance after decades of plant closures. Unlike fusion, which remains experimental and has yet to generate more energy than it consumes, fission is the established technology behind all existing nuclear power plants.
For tech giants, nuclear fission offers a stable, continuous energy supply that operates 24/7, allowing data centers to run computational loads whenever needed.
But what’s especially exciting are the new designs of small modular reactors (SMRs), which address many limitations of traditional nuclear plants. While older reactors were massive, often exceeding 1 gigawatt, SMRs consist of multiple smaller modules that can be deployed together to meet varying demands.
SMRs aim to reduce costs through mass manufacturing, but none have yet been built in the U.S. Still, this hasn’t deterred Amazon, Google, Meta, and Microsoft—they have either invested directly in nuclear startups or signed power purchase agreements with them, or both.
Here’s a look at the leading nuclear fission startups supported by Big Tech:
Kairos Power
Google has placed a major bet on Kairos Power, committing to purchase roughly 500 megawatts of electricity by 2035, with Kairos’s first reactor slated to come online by 2030.
Kairos’s SMRs use molten fluoride salt both for cooling and heat transfer to steam turbines. The high boiling point of the salt allows operation at low pressure, enhancing safety. The reactor’s fuel consists of carbon- and ceramic-coated pebbles designed to withstand meltdown scenarios.
Based in Alameda, California, Kairos has received $629 million in government funding—including $303 million from the U.S. Department of Energy. In November 2024, the U.S. Nuclear Regulatory Commission approved the construction of two 35-megawatt test reactors in Tennessee, smaller than the company’s planned 75-megawatt commercial units.
Oklo
Oklo focuses on SMRs tailored for data centers and was backed by OpenAI CEO Sam Altman, who also took the company public via a reverse merger in July 2023. Altman served as Oklo’s chairman until April 2024, stepping down as OpenAI entered negotiations to secure energy from Oklo. Previous investors include DCVC, Draper Associates, and Peter Thiel’s Mithril Capital Management.
Oklo’s reactors use liquid metal cooling and are based on a U.S. Department of Energy design aimed at minimizing nuclear waste. Although Oklo’s first license application was rejected in January 2022, the company plans to resubmit in 2025. Meanwhile, Oklo secured a deal to supply 12 gigawatts of power to data center operator Switch by 2044.
Saltfoss
Formerly known as Seaborg, Saltfoss also develops SMRs cooled by molten salt but envisions placing two to eight reactors on a ship, creating a “Power Barge.” The startup has raised nearly $60 million, including seed investments from Bill Gates, Peter Thiel, and Unity co-founder David Helgason. Saltfoss has partnered with Samsung Heavy Industries to build both the ships and the reactors.
TerraPower
Founded by Bill Gates, TerraPower is developing a larger-scale reactor called Natrium, cooled by liquid sodium and equipped with molten salt energy storage.
Construction began in June 2024 on the first Natrium power plant in Wyoming. The reactor is designed to produce 345 megawatts—smaller than other new nuclear plants but larger than most SMRs.
What sets Natrium apart is its molten salt heat storage system, which allows the reactor to operate steadily regardless of fluctuating demand. Excess heat is stored in molten salt and can be later converted to electricity when needed.
Investors include Gates’s Cascade Investment, Khosla Ventures, CRV, and ArcelorMittal.
X-Energy
X-Energy secured $700 million in Series C-1 funding last year, led by Amazon’s Climate Pledge Fund. The company announced two development agreements to deploy 300 megawatts of nuclear capacity in the Pacific Northwest and Virginia.
X-Energy’s high-temperature gas-cooled reactors buck current U.S. and European trends favoring other designs. Its Xe-100 reactor is expected to generate 80 megawatts. Helium gas circulates through the reactor’s 200,000 fuel “pebbles,” absorbing heat to drive a steam turbine.
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