2025 Climate Tech Companies to Watch: Kairos Power and its next-generation nuclear reactors
Like many new nuclear startups, Kairos promises a path to reliable, 24/7 decarbonized power. Unlike most, it already has prototypes under construction and permits for commercial reactors.
Kairos made last year’s list because of a safer design for small modular reactors that produce power from nuclear fission. The company uses molten salt to cool its reactions and transfer heat, rather than the high-pressure water that’s used in existing fission reactors. The company was moving fast but cautiously, planning a series of non-nuclear prototypes to explore how best to pump this special coolant, a mixture of fluorine, lithium, and beryllium.
That iterative process continues today, with the recent installation of a non-nuclear reactor vessel for Kairos’s third test unit at the historic Oak Ridge nuclear site in Tennessee. The unit will test the handling of the coolant and the company’s innovative fuel—golfball-sized pebbles that package tiny seeds of uranium within a series of carbon and ceramic shells. This fuel was developed by the United Kingdom and the US Department of Energy (DOE), which has committed up to $303 million to support the construction of a reactor called Hermes, currently underway at the site.
Ultimately, Kairos expects the combination of its fuel and special coolant to enable commercial reactors that are cost-competitive with natural gas plants and boast safer operation than conventional reactors, even in the event of complete power loss.
Key indicators
- Industry: Nuclear power
- Founded: 2016
- Headquarters: Alameda, California, USA
- Notable fact: In 1954, Oak Ridge National Laboratory in the US was home to the first molten salt reactor, an experimental power source for a possible supersonic nuclear aircraft.
Potential for impact
With sharp cuts to US federal funding for solar and wind projects, nuclear power is one of the few zero-carbon technologies that still attract bipartisan political support. Although developing new systems is slow and expensive, nuclear reactors excel at providing 24/7 baseload power that can replace fossil fuel plants.
Small modular reactors like the ones Kairos is building are particularly attractive for places that require steady amounts of power or lack reliable transmission infrastructure. They can operate around the clock in any weather conditions, and they are largely independent from the grid.
Applications could include AI data centers, whose electricity consumption the International Energy Authority expects to more than double over the next five years, but also remote towns and safety-critical transportation hubs. Denver International Airport announced recently that it was exploring the possibility of constructing one such reactor, after over 1,000 flights at London’s Heathrow Airport were grounded or diverted earlier this year due to a substation failure.
Caveats
Although there have been numerous experimental molten salt reactors, no one has yet shown that they can operate one consistently and profitably over the long term. Building test reactors in parallel might shorten Kairos’s development cycle, but it could also reveal problems that cascade through the entire fleet.
Furthermore, Russia’s invasion of Ukraine in 2022 slammed the doors on supplies of Russian uranium, including the fuel with a higher concentration of uranium-235 that’s needed to make the pellets for Kairos’s efficient reactors. The US and Europe have since been scrambling to mobilize domestic production, but the process will take years. In the meantime, the DOE has agreed to supply Kairos and a few other US companies developing similar reactors with limited quantities of the specialized uranium for their near-term fuel needs.
Even with a regular supply, transporting that uranium to reactors won’t be straightforward. There isn’t yet a special container approved by the US Nuclear Regulatory Commission that could move it in any significant volume, and using existing containers could take thousands of shipments to fuel a single reactor. Kairos has said that it could potentially use a less enriched type of uranium to prove its technology’s viability while the supply of its desired version is tight.
Next steps
Kairos is now building three reactors simultaneously —two non-nuclear test units to validate its systems, and the Hermes experimental nuclear reactor. These facilities will prove the molten salt technology at full scale, without generating any usable power. Kairos will soon start work on another, Hermes 2, which will be the company’s first system to produce electricity.
When that 50-megawatt reactor comes online in 2030, Kairos will sell its power to the Tennessee Valley Authority, the US’s largest public power provider, and the associated clean energy credits to Google. Google has agreed to purchase up to 500 megawatts of generation capacity from Kairos by 2035 to help decarbonize its data centers. But take all those dates with a pinch of molten salt—nuclear power stations usually come in late and over budget.
