Small modular nuclear reactors are having their moment.
The Trump administration is pushing to speed up development. The likes of Google and Meta are signing on. In Colorado, the law now counts nuclear as clean energy and Colorado Springs and Pueblo County are considering the technology.
A Pueblo advisory committee even concluded that after Xcel Energy’s coal-fired Comanche power plant closes, the community can only be “made whole,” with a small modular reactor, or SMR.
The Denver International Airport briefly flirted with the idea of an SMR to power the airport’s growth.
The only thing missing is an actual SMR. In the U.S., one has won building permits and others are close, but to see an operating SMR one must head to Russia or China. They each have one. Japan has a test reactor.
And an SMR isn’t one thing. Some are microreactors, as small as 5 megawatts. Some are 345 MW. Some will float, one gets buried underground, another one could ride around on a flatbed truck.
They use different nuclear fuels, including heavily enriched uranium, and different coolants from water to gas to molten metal to molten salt.
In a word, SMRs are not one but many ideas. There are about 50 different types under development worldwide, according to the International Atomic Energy Agency, or IAEA, including 15 in the U.S.
Many are working on the concept
The companies pursuing SMRs range from start-ups with a handful of employees to Westinghouse, GE Vernova Hitachi and Rolls Royce.
The idea of a nuclear Lego set — where modules are built in a factory, transported to a site “as small as a parking lot” and plunked down ready to go — is appealing. If one module is 80 MW, simply connect three for a 240 MW plant.
SMRs, proponents say, also come with inherent safety features. Some can operate at higher temperatures than the traditional big reactors producing electricity more efficiently and run for years without refueling.
The SMR could fill four key niches, according to the IAEA: a replacement for coal on the electric grid, providing process heat for industry, replacing diesel engines for mining and powering data centers.
Critics, however, question whether the costs of these untested technologies will ever be competitive and for some designs, a commercial source of fuel doesn’t even exist. They will also create new and complex forms of nuclear waste.
And they will not be ready in time to help with the surge in electricity demand the country is facing. ICF, an industry consultant, forecasts a 25% increase in load by 2030, spurred primarily by data center demand.
In Colorado, Xcel Energy projects a 19% increase in peak demand by 2030.
“Does SMR technology address energy needs?” asked Allison Macfarlane, the former chair of the Nuclear Regulatory Commission. “No, it doesn’t, it won’t. There’s no way that they can. They just cannot bring these to commercial scale in 10 years.”
For the moment everyone agrees cost is an issue.
18 times the cost of solar
The first SMR was scheduled to be built in the U.S. by NuScale Power but the project was cancelled as costs doubled between 2015 and 2023 to $21,561 a kilowatt, according to a study by the Institute for Energy Economics and Financial Analysis or IEEFA.
By way of comparison, the installed cost of utility-scale solar in 2023 was $1,200 a kilowatt, according to the National Renewable Energy Laboratory.
“Certainly, first-of-time, costs are higher,” said Erik Cothron, a senior analyst with the Nuclear Innovation Alliance, a nonprofit promoting nuclear development. “If you can build 10 of them you can spread those first-time costs… and get away from just building these things one at a time.”
So, the development of SMRs is a race among competing technologies and companies that will likely be run over more than a decade to determine a winner or winners, who can get their designs up and running and their costs down.
“Of all the different technologies and the companies that we’re looking at, not all of them will succeed. Many of them will fail,” Cothron said. “In fact, we do not want an advanced reactor ecosystem where we have several dozen designs being commercialized. To reduce costs, we need to build the same thing over and over again.”
The shake-out will take years, said Jess Gehin, the associate director for nuclear science and technology at the Idaho National Laboratory. He estimated the first full-size SMR reactors will start between 2028 and 2030, with commercial use by 2035. Then it is a question of which technology wins.
“This is what happened back in the early days of nuclear, there were a number of designs, and in the end, the light-water reactor emerged,” Gehin said. Today, 90% of the nuclear power plants in the world, including 63 in the U.S., use pressurized light-water reactors, which use water under pressure as the coolant.
“One of the big bottlenecks will be the fact that you may need $300 million to $400 million just to get a prototype built and get it licensed,” said James Walker, CEO of Nano Nuclear Energy, an SMR start-up.
“So, there’s obviously going to be a big squeeze on companies’ ability to be able to do that,” Walker said. “They will narrow things down.”
The question, said Dennis Wamsted, an analyst with the clean-energy oriented IEEFA, is “how many have to get built before some of them fall by the wayside … and how long does it take the winner to ramp up?”
Big utilities are betting on the tech
The uncertainty hasn’t dissuaded some big names from placing their bets on these nascent technologies.
The federally-owned Tennessee Valley Authority, or TVA, the country’s largest public electricity provider, has applied to the Nuclear Regulatory Commission for a permit to build a GE Vernova Hitachi Nuclear Energy SMR, the BWRX-300.
The 300-MW reactor is a mini-me version of a standard light-water reactor. Several other companies, including NuScale, have similar light-water technology.
“The closer you are to conventional light-water reactors, the easier time you’re going to have,” said Mark Jensen, the head of the nuclear science and engineering program at the Colorado School of Mines.
The designs have been proven; there is operating experience with the technology and the uranium oxide fuel is already manufactured in the U.S., Jensen said.
Duke Energy and American Electric Power, two of the country’s largest investor-owned utilities have also expressed interest in BWRX-300 and one is under construction in Canada.
These reactors, however, have the same drawbacks as their bigger brother. They are large enough that siting is an issue. “The bigger they are the greater the risk of cost overruns,” IEEFA’s Wamsted said.
The reactors must be pressurized so the water does not boil off. Loss of coolant could, in theory, lead to a meltdown. But Jensen said that passive safeguards and the smaller size means there “wouldn’t be something like Fukushima,” referring to the 2011 nuclear disaster in Japan.
“You can get it small enough that that heat that’s there, even when you turn the reactor off, can dissipate out into the environment without exceeding these critical temperatures,” he said
The TVA, a leader in promoting SMRs, has also signed an agreement to buy as much 6 gigawatts of power from a string of NuScale reactors — although there is no timeline for when they will operate.
In addition, the TVA and Google have signed a development agreement with Kairos Power to build a 50 MW plant, in Oak Ridge, Tennessee, a prelude to providing 500 MW of power for Google by 2035.
Kairos’ design is one of the “advanced reactors” replacing water as a coolant. The 150-MW reactor will use molten salt and an enriched fuel known as TRISO, small uranium pebbles packed together in ceramic spheres the size of golf balls.
Since the molten salt doesn’t evaporate the reactor doesn’t need to be pressurized and can run at higher temperatures. The enriched TRISO fuel is resistant to meltdown.
A Russia problem and a waste problem
However, the only source of this enriched uranium is Russia and the import of the fuel was banned in 2024, in part to spur domestic development, with the federal government providing $3.4 billion in funding. There is still no commercial source of the fuel.
TerraPower, the reactor company founded by Bill Gates, also uses a molten-salt coolant and avoids the enriched uranium dilemma while creating other challenges.
The company has applied for a license to build a 345 MW reactor in Kemmerer, Wyoming and in August signed an agreement with the Utah Office of Energy Development to look for a site in that state.
Gates isn’t the only Silicon Valley entrepreneur in the game. Sam Altman, the CEO of OpenAI was an initial backer and chairman of Oklo which is developing a 75 MW, liquid-metal-cooled reactor that can use recycled waste nuclear fuel.
On Sept. 4, Oklo announced plans to build the country’s first private fuel recycling facility in Oak Ridge and is “exploring opportunities” to recycle fuel from the TVA’s three large nuclear power plants.
“Fuel is the most important factor in bringing advanced nuclear energy to market,” Oklo CEO Jacob DeWitte said in announcing the plan.
The fuel, however, may be these reactors’ Achilles heel. “The problem is, with these more exotic fuels some of them may not be stable,” Macfarlane said.
For example, Kairos’ plan to mix its radioactive fuel in with its molten-salt coolant will create an entirely new kind of waste that needs to be processed, Macfarlane said.
The TerraPower design uses a sodium bond to seal the uranium to a metal fuel assembly.
“The sodium-bonded spent metallic fuel creates challenges for disposal, as the sodium is highly reactive and cannot be easily separated from the fuel elements, necessitating specialized treatment to prevent chemical reactions and safely isolate the radioactive material,” according to an NIA report.
One thing these enriched fuels are trying to do is deal with “neutron leakage,” Macfarlane said. “This is just a physics issue.”
A nuclear chain reaction starts when a neutron hits a uranium 235 atom and splits it releasing other neutrons that hit other atoms releasing more neutrons.
“When you shrink the reactor core, there’s less for those neutrons to run into, there’s less space, and therefore you simply have more neutrons leaking out of the core,” Macfarlane said.
“When you leak neutrons, the efficiency of your reactor, the ability of your reactor to produce energy goes down,” she said. One solution is highly enriched fuel which gives the neutrons more atoms to hit.
“Once you get that enriched uranium, then you have to put it into a particular type of fuel,” Macfarlane said. “So, you need a whole fuel fabrication facility. You need a new enrichment facility. You need ancillary facilities for the enrichment. You need a conversion and a de-conversion facility.”
“None of these exist, and they will all cost tens of billions of dollars to put together. That will add to the cost of the reactor,” Macfarlane said. “That’s why I say we have no idea how much these reactors will really cost.”
“I think people who get into this, get involved in this, should just be really realistic about what all the challenges are,” Macfarlane said.
Early adopters face risks
Still, one of the appeals of these enriched-fuel technologies is that they can run at temperatures double or nearly triple the 300 degrees Centigrade of a light-water reactor.
“The advantages of some of these technologies are that reactors can operate at a higher temperature, so they can produce electricity more efficiently, have a higher energy efficiency, or produce heat that can be used for an industrial process,” the Idaho lab’s Gehin said.
Another entrant, X-Energy, which is developing a gas-cooled, 80 MW reactor using TRISO fuel, is partnering with chemical maker Dow to provide steam and electricity at one of its complexes on theTexas Gulf Coast.
SMRs are also getting a boost from the Trump administration, with four executive orders promoting nuclear energy. Nuclear energy tax credits were preserved in the “One Big Beautiful Bill Act,” while those for wind and solar were cut.
In August, the Department of Energy picked 11 SMR projects to fast-track with the goal of having at least three small test reactors up and running by the country’s 250th anniversary on July 4, 2026. The winners include Oklo and Last Energy.
“They’re going to be tiny,” said IEEFA’s Wamsted. “They’re not going to solve anybody’s problems.”
Still, there is budding interest in Colorado. The bill designating nuclear energy as a clean energy source opened up the possibility of local clean energy financing and said SMRs “can produce higher quantities of clean energy with a smaller land footprint.”
The reactors, the bill said, “can replace coal power plants while maintaining the number of jobs in the communities.”
In Colorado Springs, a citizen advisory committee recommended that the municipal Colorado Springs Utilities “create a roadmap and research plan to develop a basic knowledge of nuclear power options focusing on SMRs.”
“Nuclear will continue to be evaluated as part of our Integrated Resource Plan process,” utilities spokesperson Danielle Nieves said in an email.
Pueblo County has pushed for an SMR as a replacement for the Comanche Station coal-fired power plant — the county’s biggest taxpayer — excoriating the Colorado Public Utilities Commission for failing to “even consider innovative technologies, such as advanced nuclear, for coal communities.”
In response to Pueblo County’s critique, and its intention to ask the Trump administration to order the Comanche plant to keep running, the PUC said it would take another look at SMRs.
Early adopters, however, will run costly risks, IEEFA’s Wamsted said. “It’s not very realistic to expect these SMRs to come out of the box and on day one run at 90% capacity,” he said.
“Regulators are going to say, ‘OK Xcel, you can be number 10 on the list, but you’re not going to be 1, 2, 3 or 4, because somebody else is going to take the risk of that cost overrun,” Wamsted said. “
The Comanche 3 coal-fired unit is slated to close in 2031. When it opened in 2010 the plant employed state-of-the-art “clean coal” technology, but from its start the $1 billion plant was plagued with breakdowns and shutdowns.
The plant has been closed for the equivalent of two years — including all of 2020 and the end of this past July — making it the most expensive plant on the Xcel system.
One place there won’t be an SMR is at Denver International Airport. On Aug. 6, Mayor Mike Johnston and airport CEO Phil Washington announced a $1.5 million plan to evaluate adding an SMR to the airport. Two weeks later, the plan was shelved as it faced local opposition.
“A million dollars,” Macfarlane said. “Wow, I could use a million dollars. I could give them an answer.”
And Cothron, the Nuclear Innovationa Alliance analyst, said, “I don’t foresee in the near future that advanced reactors will be used directly behind the meter to power airports, because the first of a kind are going to be very costly.”
“We are looking for them to be used on the commercial grid and data centers,” he said.
Days after abandoning the SMR study, DIA announced plans for an 18 MW solar array that would cover 90 acres making it the largest in Denver.