Groundbroken on a Cold War ghost town in Oak Ridge on April 17, 50 megawatts of fluoride salt now rising from Tennessee soil carry a self-sealing trick that no water cooled reactor in America has ever managed
On a Thursday morning in April 2026, shovels broke Tennessee ground on a site that once held the largest uranium enrichment complex the world had ever seen. The occasion was a groundbreaking. The machine going into the earth, though, was something genuinely new. It runs on a coolant that, under certain conditions, simply turns to stone. And the electricity it will eventually generate has already been sold to one of the most power hungry companies on earth.
A campus rising from Cold War concrete
The East Tennessee Technology Park sits on the western edge of Oak Ridge, on land the federal government quietly acquired in the 1940s and never really gave back. For decades, enormous gaseous diffusion buildings enriched uranium for both weapons and reactors. The last of those buildings shut down in 1985, and the cleanup that followed stretched across two generations, leaving behind a wide, flat brownfield edged by Appalachian hills where the ground carries history in every layer of soil.
Rising from the footprint of the historic Oak Ridge Gaseous Diffusion Plant, the project will continue the region’s distinguished nuclear legacy and promote its resurgence as a hub for advanced nuclear innovation. The site already hosts Hermes 1, the first non light water reactor permitted for construction in the United States in more than 50 years. Into this context, on April 17, Kairos Power drove the ceremonial first shovel for Hermes 2, the larger sibling that will actually put electrons on the grid.
The salt is still liquid, the foundation is still curing, and 2030 is still four years away, but the ground is broken, and in Oak Ridge, that means something.
A reactor that learned to walk before it ran
Kairos Power broke ground on Hermes 2 having received test reactor construction permits from the Nuclear Regulatory Commission in November 2024. The two reactors share a campus but serve different purposes. Hermes 1 is a low power machine designed purely to prove the technology and gather operating data. Hermes 2 is where the power actually flows.
Plans shifted when a power purchase agreement between the Tennessee Valley Authority and Google prompted the company to announce a change to a 50 megawatt electric output for the Hermes 2 site. In the world of advanced reactors, that is a full commercial demonstration, the step where theory meets a real power bill. Kairos expects Hermes 2 to begin operations by 2030, when the fluoride salt cooled high temperature reactor could become the first NRC licensed non light water reactor to produce commercial power.
The number that changed and the man who explained why
An approved amendment extends the completion date for the Hermes test reactor facility from December 31, 2026, to April 30, 2029. That is a two year slip, a reminder that regulatory realism and engineering ambition do not always move at the same pace. What keeps investors steady is the deliberate structure of the whole program.
Kairos built three non nuclear Engineering Test Units before a single shovel of nuclear side earth was turned. Each unit taught the team something about how salt flows, how pipes seal, how the reactor vessel settles. Those hardware demonstrations were designed to test system integration and generate operating experience across the entire Hermes reactor series. The CEO put the philosophy plainly: “For nuclear projects to be successful, we need more than just the right technology,” said Mike Laufer, Kairos Power cofounder and CEO. “We need to understand every aspect of project delivery. Hermes 2 is where that all comes together.”
What the coolant actually does, and why it rewrites the safety conversation
Most commercial reactors in the United States use ordinary water to carry heat away from the fuel. Water works, but it must be kept under enormous pressure, sometimes 155 times atmospheric pressure, to stop it from flashing to steam inside the vessel. If that pressure boundary fails, cooling stops fast.
Hermes will use a TRISO fuel pebble bed design with a molten fluoride salt coolant. The salt, a lithium beryllium compound, melts at around 460 degrees Celsius and runs through the core as a liquid. If circulation pumps stop, the salt does something water cannot: it cools, thickens and solidifies around the fuel, encasing it. There is no steam explosion, and the physics of the material itself becomes the safety system. This is the hidden catch inside something genuinely promising: the entire supply chain for fluoride salt components, which barely exists today, has to be built alongside the reactor. Oak Ridge is not just proving the machine; it is proving the industry around it.
A town, a tech giant, and a long horizon
Oak Ridge has lived alongside nuclear energy longer than almost any community on earth, and residents there tend to read project timelines with the patience of people who have watched grand promises stretch across decades. The Hermes 2 groundbreaking drew elected officials, community members, and partners to the site, carrying the atmosphere of a genuine civic moment rather than a press release.
The Google connection adds a layer that few nuclear projects have ever carried. The Hermes 2 reactor will provide energy to a Google data center via a power purchase agreement with Tennessee Valley Authority, meaning the electricity has a named buyer before a single kilowatt has been generated. That commercial structure is one that advanced nuclear procurement programs across the country are now trying to replicate. The U.S. Department of Energy will invest up to $303 million through a performance based milestone contract funded by the Advanced Reactor Demonstration Program, meaning the money follows results, not promises. The salt is still liquid, the foundation is still curing, and 2030 is still four years away, but the ground is broken, and in Oak Ridge, that means something.
Hugo is an engineer with strong technical expertise. Multilingual from an early age, his writing combines technical clarity with a strong interest in science and energy.
