Meet the only US company building an advanced reactor
Published: July 29, 2025 06:50 AM EDT
Author: Francisco "A.J." Camacho
TL;DR
• Kairos Power is the only U.S. company currently constructing a small modular nuclear reactor, using an experimental molten fluoride salt cooling system and taking a "rapid iterative design" approach with multiple demonstration reactors • The company has achieved significant regulatory milestones, becoming the first to receive a construction permit for a Generation IV reactor and pouring the nation's first advanced nuclear concrete, with backing from Google • Kairos faces a critical challenge in securing a reliable supply of high-assay, low-enriched uranium (HALEU) fuel, which is not yet commercially produced in the U.S. and currently relies on restricted Russian imports
---
Second in an occasional series on companies leading the way on small nuclear reactors.
Kairos Power is the only company in the country actively building a small modular nuclear reactor.
The California startup got there while taking a moonshot approach, betting on two commercially unproven technologies at once: modular design and nonwater cooling. The experimental reactor it is building in Tennessee uses molten fluoride salt as a coolant — a Generation IV technology so far commercially untested.
That's a risky move in an uncertain market where other promising advanced nuclear ventures have stumbled. But Kairos leaders think they can succeed by moving beyond the drawing board and starting to build demonstration after demonstration.
"It does take time to stand up these capabilities, but when you stand them up and you've actually gone through those kinds of learning curves and those kinds of scar tissues that you get, we now have a very capable team that's able to deliver and do a lot more," said Edward Blandford, Kairos' co-founder and chief technology officer, during a tour of the company's Albuquerque Manufacturing Campus in New Mexico.
Kairos argues that vertically integrating its supply chain — and doing everything from fuel fabrication to welding reactor vessels itself — gives it a better shot at staying on schedule. One of its test reactors, dubbed "Hermes," has already secured the first-ever construction permit for a Generation IV reactor from the Nuclear Regulatory Commission, and Kairos has poured the nation's first advanced nuclear concrete.
That iterative, start-small approach has won over some high-profile backers. Google inked an agreement with Kairos last year, signaling confidence in the startup's direction and potential relevance to the data center boom.
The risks are still high. In October, Ultra Safe Nuclear Corp. —a rival startup pursuing microreactors and advanced fuel — filed for Chapter 11 bankruptcy despite years of government and private support.
Kairos' success hinges on whether the U.S. and Europe can stand up their own supply chain for high-assay, low-enriched uranium. The company needs HALEU to make its reactor's TRISO fuel with the energy density intended for the design.
HALEU is not yet commercially produced in the U.S., which currently relies on imports from Russia that have been heavily restricted since the Russian invasion of Ukraine in 2022.
"They at least are building a demo model, but they need TRISO fuel with HALEU — a heavy lift to make commercial," said Allison Macfarlane, a former chair of the NRC.
A propitious moment for action?
On a recent sunny June day, Martin Bryan parked his company ATV in a spot that overlooked a construction site triangled between an old railyard, rows of electrical transmission lines, and a tree-lined creek. The Oak Ridge construction site is expected to soon host the first commercially owned Generation IV nuclear reactor in North America.
Bryan, Kairos' director of site integration in Tennessee, describes the company's "overall philosophy" as "rapid iterative design."
"That's kind of something that our founders picked up from SpaceX," Bryan said. "Rather than take 10 years to build one big rocket, every year you build a couple of smaller ones. See what works, what didn't work. And then we keep scaling that."
Kairos already has engineered one test unit and is working on two more. Such reactors are built to test certain systems like coolant pumping without using nuclear material.
The company is also constructing two demonstration reactors in Tennessee. Hermes will test their design's most basic mechanics, with Hermes 2 incorporating electricity generation and other systems. With construction permits from the NRC for both, Kairos has already begun pouring concrete and welding rebar at the site.
As of July, Hermes is the only SMR under construction in North America, according to the World Nuclear Association.
Founded in 2016 by three University of California, Berkeley, engineers, Kairos believes that advanced nuclear technologies demonstrated in laboratories for decades have reached a "kairos." The company's Greek name translates to a propitious moment for action — or, more simply, an opportunity.
"AI demand, cloud computing, data centers: Those are going to strengthen the case for SMRs, and they serve as an important catalyst to help bring them to market," said Peter Hastings, vice president of regulatory affairs at Kairos. "Apart from AI, and even apart from data centers more broadly, we're witnessing a massive push for additional electricity from industries, from transportation, air conditioning, heating — all moving away from fossil fuels, and increasing the need for firm, carbon-free electric power."
Many nuclear industry observers say Kairos is leading the field to capitalize on that opportunity. Macfarlane commended the company's iterative design approach and regulatory A-team.
"I've really been impressed with Kairos," said Macfarlane. "They have shown a lot of smarts in terms of their approach, getting the part 50 construction license, moving ahead with that. That's great. That's how it should be done, and I think Kairos is the example to everyone else of how to do it right."
NRC critics say the agency's licensing process is too slow and bogs down innovation, but defenders of the agency point to Kairos as proof that the process is getting faster — especially with thorough applications. A construction application typically takes multiple years for the agency to review, but Kairos got the green light for Hermes 2 last year after just 18 months.
"Your application can go through quite quickly — and Kairos' did — if you submit, to begin with, a very high-quality application. There will always be, and there should always be, questions from the regulator about your application," Macfarlane said. "When you get those questions, you'd best have the capability to answer the questions with high-quality responses. That's what Kairos did, and they went through really quickly."
Kairos' quick turnaround was also attributed to procedural reforms within the commission and the application being for a demonstration reactor that won't service the grid.
One big hurdle
But the best-laid plans often go awry, especially in the nuclear field where supply chains are complex and timelines long. Nuclear giant Westinghouse Electric declared bankruptcy in 2017, largely due to hiccups in a single reactor model — the AP1000.
For Kairos, the tallest hurdle is fuel, according to Macfarlane and Brian Wirth, head of the University of Tennessee's Department of Nuclear Engineering. The university opened a nuclear training laboratory with an endowment from Kairos in February.
"The one thing that I had always been a little bit concerned about for them was, much like all the advanced reactor companies that are focused on TRISO, how they were going to source their TRISO," Wirth said.
Half of the company's solution is back in New Mexico at the pebble development lab and TRISO development lab on Kairos' manufacturing campus. In an interview at the campus, Blandford held out a nonradioactive model of the TRISO "fuel pebble" — a golf-ball-sized graphite sphere.
Blandford said the company already has arrangements to work with Los Alamos National Laboratory to fabricate TRISO. But he acknowledged that getting Kairos' hands on the HALEU that gets manufactured into TRISO is "an open-ended question right now."
"The U.S. is standing up that capability right now," Blandford said. "DOE is in the place where they're allocating high-assay LEU for certain smaller reactors, like us."
"All signs point to the government pursuing HALEU production on the timescales when we need it," he continued.
In April, the Department of Energy announced plans to provide HALEU to Kairos and four other U.S. nuclear developers "to meet their near-term fuel needs."
Blandford said that the Los Alamos lab's Low-Enriched Fuel Fabrication Facility will receive that material soon and is on track to receive its safety authorization in the next six months — while Kairos expects to start producing TRISO kernels for Hermes in 2026.
He added that HALEU isn't strictly necessary for reactor operation.
"We are in the process of obtaining LEU+ to serve as a bridge," Blandford said. "[Kairos's reactor] operates most efficiently with HALEU; however, it can use a range of enrichment levels to prove the technology's commercial viability while we wait for HALEU to become more widely available."
But finding long-term HALEU remains a challenge for the American nuclear industry.
Centrus Energy has started producing small amounts of HALEU in Ohio and hopes to scale up production to commercial levels. Still, Centrus says it is at least three and a half years from a full-scale HALEU production line, and it is dependent on "securing the funding to do so."
A British HALEU plant is also in the works, but it's not expected to come online until 2031.
Despite the outstanding concerns around uranium supply, Wirth at the University of Tennessee said he is "optimistic" about Kairos. He pointed to the company's vertical integration strategy, engineering skill, self-sufficiency in fuel fabrication and regulatory engagement as setting "the example" for nuclear developers.
"I think they have as good a shot as anybody of really getting to a point where we could see multiple orders," Wirth said.
AI Analysis
Kairos Power represents a fascinating case study in advanced nuclear technology, demonstrating both the potential and challenges facing next-generation reactors. Their "rapid iterative design" approach, borrowed from SpaceX, offers a refreshing alternative to traditional nuclear development's lengthy timelines and massive upfront investments. The company's success in navigating regulatory hurdles and achieving construction milestones suggests that with proper execution, advanced nuclear technology can move from laboratory to reality. However, their dependence on HALEU fuel exposes a critical vulnerability that extends beyond any single company to the broader U.S. nuclear industry's strategic independence. The timing of their progress, coinciding with surging AI and data center electricity demands, could prove fortuitous if they can resolve their fuel supply challenges.
