Artificial intelligence has sent demand for electricity skyrocketing in the U.S. after years of virtually zero growth. That has sent Big Tech companies scrambling to secure generating capacity for their data centers.
For many, that has meant turning to nuclear fission. The power source has been experiencing a resurgence in the last few years following decades of plant closures. (Fission, used in all current nuclear plants, is distinct from fusion, the still-experimental approach to getting power from atoms that, while attracting investors, has yet to produce more electricity than it consumes.)
For tech companies, part of the appeal of fission is a stable, predictable source of power that flows 24/7, giving their data centers the potential to run computing loads whenever they require it.
But another part of the appeal lies in new reactor designs that promise to overcome the shortcomings of existing nuclear power plants. Where old power plants were built around massive reactors that could generate over 1 gigawatt of electricity, new small modular reactor (SMR) designs see multiple modules deployed alongside each other to meet a range of needs.
SMRs rely on mass manufacturing to bring costs down, but to date, no one has built one in the U.S. Still, that hasn’t kept Amazon, Google, Meta, and Microsoft away from the table. They’ve either signed agreements to buy power from nuclear startups or invested in them directly — or both.
Here are the nuclear fission startups backed by Big Tech.
Kairos Power
Kairos Power received a vote of confidence from Google when the search giant promised to buy around 500 megawatts of electricity by 2035, with the first reactor targeted to come online by 2030.
The company’s small modular reactors rely on molten fluoride salt for cooling and to transport heat to a steam turbine. The salt’s high boiling point means that the coolant doesn’t need to be kept at high pressure, which should improve operating safety. The reactors contain fuel pebbles coated in carbon and ceramic shells, which should be strong enough to withstand a meltdown.
The Alameda-based startup has received a $629 million award from the U.S. government, including $303 million from the Department of Energy. In November 2024, Kairos received approval from the U.S. Nuclear Regulatory Commission to commence construction on two reactors in Tennessee. At 35 megawatts, the test units will be smaller than Kairos’ eventual commercial reactors, which are expected to generate 75 megawatts each.
Oklo
Oklo is another SMR company targeting the data center world — no surprise given that it was backed by OpenAI CEO Sam Altman, who also took the nuclear startup public via a reverse merger with his special purpose acquisition vehicle, AltC, in July 2023. Altman served as chairman of Oklo until April, when he stepped down as OpenAI began negotiating with Oklo for an energy supply agreement. DCVC, Draper Associates, and Peter Thiel’s Mithril Capital Management are among the startup’s previous investors.
Cooled by liquid metal, Oklo’s reactor is based on an existing U.S. Department of Energy design that’s intended to reduce the amount of nuclear waste that results from regular operations. Still, Oklo’s path hasn’t been a smooth one. The company’s first license application was denied in January 2022. Oklo has said it will resubmit the application sometime in 2025. But that hasn’t stopped the company from landing a deal to supply data center operator Switch with 12 gigawatts by 2044.
Saltfoss
Like Kairos, Saltfoss, formerly known as Seaborg, also wants to build SMRs cooled by molten salt. But unlike Kairos and others, it envisions placing two to eight of them on a ship to create what it calls a Power Barge. The startup has raised nearly $60 million, including a $6 million seed round that included investments from Bill Gates, Peter Thiel, and Unity co-founder David Helgason, according to PitchBook. Satlfoss has an agreement with Samsung Heavy Industries to build the ships and the Satlfoss-designed reactors.
TerraPower
Founded by Bill Gates, TerraPower is building a larger reactor, called Natrium, which is cooled by liquid sodium and features molten salt energy storage.
The company broke ground on the first power plant in June 2024 in Wyoming. The Natrium design calls for the reactor to generate 345 megawatts of electricity. That’s smaller than other new nuclear plants today but larger than most SMR designs.
But Natrium has a trick up its sleeve with its molten salt heat storage system. Since nuclear reactors operate best at a steady state, the Natrium reactor can continue breaking atoms when demand is low, and the extra energy is stored as heat in a vat of molten salt, which can be drawn upon later to generate electricity.
Investors include Gates’ Cascade Investment fund, Khosla Ventures, CRV, and ArcelorMittal.
X-Energy
X-Energy landed a hefty $700 million Series C-1 last year led by Amazon’s Climate Pledge Fund. At the same time, the SMR startup announced two development agreements that would see the deployment of 300 megawatts of new nuclear generating capacity in the Pacific Northwest and Virginia.
The company’s high-temperature, gas-cooled reactors buck recent trends in the U.S. and Europe, where the design has been shunned in favor of other approaches. The company’s Xe-100 reactor is expected to generate 80 megawatts of electricity. Helium gas flows through the reactor’s 200,000 billiard ball-sized fuel “pebbles,” absorbing heat to spin a steam turbine.
