2024 Climate Tech Companies to Watch: Kairos Power and its molten salt–cooled nuclear reactors

Kairos is trying to reinvent nuclear power. Its molten-salt-cooled reactor could generate safe, reliable, carbon-free electricity that’s potentially as cheap as power generated from natural gas.

The nuclear industry in much of the world can seem stuck 30 years in the past, thanks to an outdated fleet of huge fission reactors that remain expensive to build and operate and are haunted by safety concerns. Kairos wants to change that with small, safe, modular reactors that could be cost-competitive with the cheapest fossil fuel—natural gas. Ironically, it hopes to use molten-salt-cooled reactors, a technology pioneered and then abandoned in the 1950s and ’60s in favor of designs that were further along at that time.

Kairos will use a molten salt called Flibe, which contains fluorine, lithium, and beryllium, to cool its fission reaction and then transport the heat it absorbs to a steam turbine to generate power. Today’s reactors use water for the same task, which requires an expensive, ultra-high-pressure containment system and is less efficient overall. Kairos also uses a modern nuclear fuel called TRISO, which is made of tiny kernels of uranium, carbon, and oxygen encapsulated within protective layers of carbon and ceramic. These particles are then embedded into golf-ball-size graphite “pebbles.” This form of fuel could enable safer, cheaper nuclear reactors, since each particle acts as its own containment system and is highly resistant to corrosion, oxidation, and melting. 

Together, the fuel and molten-salt cooling system should mean Kairos’s reactor is passively safe, so that even if power is interrupted (as it was at a fission reactor in Fukushima in 2011, to disastrous effect), the reactor will remain stable. 

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Key indicators

• Industry: Nuclear power 
• Founded: 2016
• Headquarters: Alameda, California, USA
• Notable fact: Just one of the golf ball–sized fuel pebbles used in Kairos’s reactor will generate as much energy as four tons of coal.

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Potential for impact

There is an ever-growing appetite for electricity to power low-carbon essentials of modern life, such as heat pumps and electric vehicles. Renewables like wind and solar are cheap and can come online quickly, but they can’t easily provide the 24-7 consistent power that coal and gas deliver. 

Nuclear reactors can provide consistent baseload power, but the number of traditional nuclear fission reactors coming online has slowed to a crawl, with new reactors barely replacing their aging predecessors. A new generation of safe nuclear reactors that deliver carbon-free power at lower costs could revitalize this flagging sector and provide a foundation of consistent electricity for when the sun isn’t shining or the wind isn’t blowing.

Caveats

TRISO fuel uses a special type of enriched uranium that had been sourced largely from Russia before the country invaded Ukraine in February 2022. After the invasion, the US banned uranium imports from Russia. Now the US has less than three years’ supply remaining and is scrambling to kick-start alternative uranium mining and enrichment supply chains. Delays or fuel shortages could threaten to slow or stall projects like Kairos’s reactors, although the company says it will also partner with a European consortium to source uranium.  

While the US is reducing the red tape for next-generation nuclear reactors, new systems still face a mountain of paperwork, and diverse international standards mean that selling the technology overseas could take longer still.  

Cost is another concern, as even the deepest pockets can struggle to finance capital-intensive nuclear projects over the decades it can take to clear regulatory approvals and finish construction. Another next-generation nuclear company, NuScale (which we featured on last year’s list), canceled a project last year after mounting costs and delays prompted utility companies to withdraw from an agreement to buy its electricity. Government support will only go so far, especially as solar power and battery storage keep getting cheaper. 

Next steps

In December 2023, Kairos secured a construction permit for a test reactor in Tennessee called Hermes, followed in February by a commitment for up to $303 million in Department of Energy funding to build it. Hermes will generate 35 megawatts of heat but won’t turn any of it into electricity. (A typical commercial US reactor today produces around 1,000 megawatts of electricity.) In parallel, the company is developing massive test devices to study the Flibe cooling system and other components and processes. 

Even before Hermes starts up, Kairos will begin work on Hermes 2, a 28-megawatt system that will be the company’s first to generate electricity. Kairos’s ultimate plan is to construct a 150-megawatt commercial facility, code-named KP-X. 

As always with nuclear projects, the company may face delays. Since Kairos secured the construction permit for Hermes, its completion date has already slipped a year, from 2026 to 2027. The company hopes to operate its first commercial reactor by 2030.

Explore the 2024 list of 15 Climate Tech Companies to Watch.