Nuclear Notes is produced by the Breakthrough Institute, and covers the policy, regulation, technology, and business of advanced nuclear energy in the United States and beyond.
Every Thursday, we track what’s really going on in the field: the new rules moving through the Nuclear Regulatory Commission, the advanced reactors moving from design to deployment, the companies going public and the utilities merging, and the executive orders and acts of Congress reshaping how the country builds. We explain not just what happened, but why it matters and how the pieces fit together.
A Molten Salt Reactor Gets Additional Backing
Kairos Power has raised another $643 million for its 50-megawatt demonstration reactor, Hermes 2, in Oak Ridge, Tennessee, the company announced. The company secured $368 million in private investment from backers including Google Ventures and Samsung C&T, along with $275 million in financing from the Department of Energy..
The construction permit for Hermes 2 was issued nearly two years ago, the first from the NRC for a power-producing Generation IV reactor. The company broke ground 18 months ago.
Kairos initially planned it as a test facility that would produce only heat, but in August 2025 changed the design to produce more heat and convert that into electricity. The company has not said how much it expects to spend to complete the plant.
Google signed an agreement with Kairos two years ago to purchase 500 megawatts of electricity, from multiple small units, by 2035. Hermes 2, which is supposed to be running by 2030, is the test case.
Kairos marries two technologies that are extremely heat-resistant, to create a reactor with an enormous safety margin. It uses tri-structural isotropic (TRISO) fuel, which incorporates fuel kernels into layers of heat-resistant materials, forming pebbles, which float in a molten salt that is difficult to boil and that would absorb fission products if any escaped the TRISO. The salt must reach over 1,400 degrees C before it will boil, making it a more robust coolant than water. The TRISO can handle temperatures of 1,600 to 1,800 degrees C.
The result is a high-temperature reactor, desirable because it can make high-quality heat for industrial purposes and can generate more electricity per BTU than today’s reactors. And unlike water-based reactors, a molten salt reactor runs at low pressure.
In September, Samsung C&T Engineering & Construction Group signed an agreement with Kairos to provide up to $100 million in cash and in-kind engineering services. It will work on the system that turns heat into electricity, and other “balance-of-plant” components. The intention is to “lay the groundwork for future collaboration to support scaled deployment” of a standardized commercial design.
Google’s new investment follows a pattern. Utility companies have shown increasing interest in new models of reactors that use light water, the technology that is used in current-generation nuclear energy plants. On the other hand, tech companies, which have pledged to cut their carbon footprints as they build hyperscale data centers, are backing technologies that are far more ambitious, and far different from what the utilities are accustomed to operating. They are taking the business model of their own field–frequent leaps in technology–and applying it to a much more staid industry, power generation.
“One of hyperscalers’ core principles is that they can drive innovation by taking something that isn’t perfect yet, and push it through the product lifecycle,” said Adam Stein, director of Nuclear Energy Innovation at the Breakthrough Institute.
And the hyperscalers are swimming in cash.
But the technology leap to molten salt requires perfecting several other techniques. One is pumps to move molten salt; another is a machine that can extract the TRISO pebbles, so they can be inspected and sorted. The design calls for pebbles to be removed from the bottom of the reactor and inserted at the top continuously, with equipment that will examine each one and determine when it should be replaced.
Another new technique, which could extend beyond Kairos’ technology, is pre-cast concrete blocks for radiation shielding, instead of concrete structures poured in place.
Google is not alone among tech companies backing advanced reactors. Amazon wants power from a 1-gigawatt complex of high-temperature gas-graphite reactors designed by X-energy, to be built in eastern Washington State and run by Energy Northwest, a public power agency.
Some traditional utilities have shown interest in more advanced reactors. Amazon, X-energy, and American Electric Power announced this week that they will study a plan to install 12 of X-energy’s Xe-100 reactors in Sullivan County, Indiana, southwest of Indianapolis, at the site of a coal plant that was retired in 1994.
While the utilities continue to try to calculate whether small reactors will be easier to build and thus eventually less expensive per unit output than the big ones, the Sullivan County installation has an interesting data point. With a total of 960 megawatts of capacity, it is supposed to operate with just 100 permanent staff. A reactor of that capacity today requires a staff of 600 or so.
Will a CANDU Be Built in the United States?
AtkinsRéalis Group, which manufactures key components for the Canada Deuterium Uranium (CANDU) reactor, has signed a memorandum of understanding with the state of Indiana and the Hoosier Energy Rural Electric Cooperative to explore building a cluster of up to eight CANDU reactors in the state.
There are 18 CANDU units operating in Ontario, but amid trade tensions with the United States, and to the disappointment of some Canadian nuclear advocates, Ontario Power Generation began construction in 2025 on the U.S.-designed GE-Vernova Hitachi BWRX-300. The utility plans to build four, the first light-water power reactors in Canada.
The CANDU was designed for countries with limited industrial capacity, a category that included Canada in the 1950s. In the CANDU design, fuel is loaded into pressurized tubes, so that it does not need a high-pressure reactor vessel. The moderator is heavy water, which, unlike the light water in U.S. reactors, does not absorb many neutrons from the chain reaction in the core. Light water is one reason that U.S. reactors must have enriched uranium, while CANDUs can run on natural uranium. Canada lacks enrichment capacity, but a reactor running on natural uranium bypasses enrichment concerns.
The design has met with some export success. Argentina, China, Pakistan, Romania, and South Korea operate them. India operates two and then modified the design to build several more.
But outside Canada, the most recent CANDU to be commissioned was in Romania, in 2007.
AtkinsRéalis has a modernized design, called the Monark, with a 1,000-megawatt output, but it has not been built. The model being pitched for Indiana is an older one; its announcement raises the possibility of an eight-reactor campus with a total output of 6 gigawatts. Most of the CANDUs in Canada operate in clusters.
A robot continuously refuels the reactors by sequentially opening a hatch at the end of each tube and inserting a new fuel bundle. Old bundles drop out of the other end of the tube, into water. CANDUs discharge a larger volume of spent fuel than a light-water reactor, though the total radioactivity per MWh is roughly comparable, since it scales with energy produced. The design allows refueling while online, avoiding the refueling outages that typical reactors require. The company had a public meeting with the NRC in August and has begun submitting topical reports, an early step in licensing.
Hoosier Energy has 17 member cooperatives that collectively serve more than 700,000 customers in central and southern Indiana and southeastern Illinois. The co-ops have historically been interested in nuclear energy, partly because they have access to lower-cost capital.
The idea of building a heavy-water reactor in the U.S. is not new. Vivek Ramaswamy, a biopharmaceutical entrepreneur and the Republican nominee for governor of Ohio, has co-founded a start-up called Atlas Atomics to do just that, with a new design. The company has a website with nothing but a title page; its prospects are uncertain.
But Indiana Governor Mike Braun is eager to bring nuclear energy to the state and recently announced an initiative to help communities in the state seek designation as sites for nuclear-related development.
Nuclear Gets Credited for More Reliability
The PJM Interconnection, which operates the country’s largest “deregulated” electricity market, auctions not only energy but also capacity, with utilities required to pay for capacity equal to their peak demand. The calculation is complicated, however, because different electric technologies have different levels of reliability; for example, a solar farm with 20 megawatts of capacity can’t offer that much in the marketplace, because the figure represents only the peak value on a sunny day, not a dependable output.
In the most recent rankings, based on past performance, PJM has ruled that nuclear power can count 96 percent of its capacity, up one point from the last capacity auction. Coming in second was demand response, at 91 percent, down one point. Those rankings have changed only slightly year to year, but onshore wind was devalued to 34 percent, down 7 points. Batteries with eight hours of storage came in at 71 percent, up one point, and those with six hours of storage were valued at 68 percent, also up one point. Solar with panels that do not tilt was at 7 percent, and sun-tracking solar at 10 percent.
A Sign of Progress at Natrium: Top Notch Tourists
With earth-moving equipment roaring in the background, the governor of Wyoming brought the governors of Idaho and Utah to see the TerraPower Natrium reactor project in Kemmerer, Wyoming. The governor of Idaho said he’d like that kind of reactor in his state, and Bill Gates, TerraPower’s founder, did not rule that out, as he showed the group around.
None of the three states has nuclear energy plants, although Idaho has a major Department of Energy lab, which hosts a reactor proving ground, where another advanced reactor company, Oklo, is building a small reactor.
A Uranium Enrichment Company Diversifies into Oil and Gas
Centrus Energy, the only American-owned uranium enrichment company, has bought Westerman, a company that supplies components for centrifuges and other nuclear equipment.
Centrus, which traces its roots to the old Atomic Energy Commission’s Cold War-era enrichment plants, said the $116 million purchase would improve the resilience of its supply chain. Centrus has a contract to supply high-assay low-enriched uranium to the Energy Department.
The acquisition will also diversify the company’s operations, Centrus said. Westerman makes equipment that separates oil from gas at the wellhead and filters out impurities, among other functions.
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The pebble extraction machine might be the part I'd most like to see in action. Kairos's February update says the test machine circulated 100,000 pebbles without a jam.