Tech companies want small nuclear reactors. Here’s how they’d work 

To fuel the insatiable energy appetite of artificial intelligence, tech companies are going big on small nuclear reactors. 

Last week, both Google and Amazon announced agreements with companies that are developing small modular reactors. These reactors would produce less power than current reactors, and many designs include different types of fuel or coolants, plus additional safety features.

The announcements have amplified the buzz around small modular reactors, which have attracted increasing attention in recent years, given the need for clean energy that won’t contribute to climate change. A variety of companies have sprung up to meet the need, producing a cornucopia of proposed designs for small modular reactors. 

“If you combine the need for resilient power with the need for clean power and the emerging availability of these designs, you get a great upswing in interest,” says nuclear engineer Kathryn Huff of the University of Illinois Urbana-Champaign.

Meanwhile, the U.S. government has been supporting the development of small modular reactors, further feeding interest. 

So what’s on the horizon for this potential new nuclear generation? We break down the big questions about how and why nuclear reactors are going small.

What are small modular reactors?

Commercial reactors in the United States typically produce around a billion watts of electrical power. Small modular reactors would produce less than a third of that. 

Traditional nuclear plants require massive investment up front, a hurdle that has stalled the building of new reactors in the United States for decades. The first newly constructed reactors built in the country in 30 years — two in Waynesboro, Ga., that switched on in 2023 and 2024 — cost around $30 billion. The construction was years behind schedule and billions over budget. 

By pivoting to smaller reactors, companies and policy makers aim to propel the proliferation of nuclear power, which is touted as a source of reliable energy free from greenhouse gas emissions. 

Plus, since smaller reactors produce less power, less residual heat needs to be removed to safely shut down the reactor in the event of an accident, simplifying safety systems.

With smaller reactors, Huff says, it’s easier to build components offsite in a factory and ship them where they need to go, rather than custom building them from raw materials on site. “The more you can build these reactors like airplanes rather than airports, the cheaper it’s generally going to be.”

What’s fueling interest in these reactors?

In the United States, nuclear power currently boasts support from both Democrats and Republicans, an unusual situation that has allowed the sector to thrive, even as political powers shift. “In the past 10 years, it’s been pretty consistent and growing support, and I think it’s a big deal,” says nuclear engineer Todd Allen of the University of Michigan. Nuclear energy is a pillar of the Biden administration’s plan to achieve climate goals.

Meanwhile, AI’s insatiable need for energy has created a problem for tech companies that don’t want to be seen as climate change baddies (SN: 12/11/23). Google announced October 14 that it would purchase energy from small modular reactors to be built by Kairos Power, which aims to have reactors starting up in the 2030s. And on October 16, Amazon announced an investment in the company X-energy and agreements with utility companies in Virginia and Washington state to establish small modular reactors.

And it’s not just big tech that’s interested. A 2023 agreement between X-energy and the chemical company Dow announced a small modular reactor to be built at one of Dow’s sites.

The U.S. Department of Energy has been funding development of small modular reactors. On October 16, the DOE announced $900 million in funding for deployment of small modular reactors. And both X-energy and the Bill Gates–backed TerraPower are building demonstration projects with DOE support. 

Traditional nuclear plants still play a role for the foreseeable future. On September 20, Microsoft announced a deal to restart the Three Mile Island power plant near Middletown, Pa., which shut down in 2019. (Yes, that Three Mile Island. After the infamous partial meltdown in 1979, another reactor at the plant continued operating (SN: 4/7/79).)

“Companies that traditionally shied away from mentioning nuclear energy as part of their portfolio, because they were concerned about public perceptions and potential policy blowback, are coming forward and embracing it,” says nuclear engineer Koroush Shirvan of MIT.

How is the technology different from current reactors?

Commercial nuclear reactors in the United States generally use the same type of uranium fuel and are cooled by water. But many small modular reactor designs break that mold.

The uranium used in reactors is enriched to include more of the relevant variety, or isotope, of uranium, U-235. Current reactors use uranium enriched to a few percent U-235. Many small modular reactors would use uranium enriched up to 20 percent U-235, known as high-assay low-enriched uranium, or HALEU (SN: 7/3/24). The fuel allows small modular reactors to run more efficiently than a reactor with conventional fuel. The United States doesn’t produce HALEU commercially in significant quantities, but efforts have begun to rev up, in anticipation of the need.

Some reactors use fuel that’s different in more obvious ways, too. X-energy and Kairos, for example, will use TRISO fuel: encapsulated, poppy seed–sized pellets of uranium contained within larger spheres of material, each the size of a tennis ball. The fuel is “extremely robust to very high temperatures for very long times,” Huff says. “It gives you this extra layer of defense.”

The coolant, the medium used to transfer heat from the reactor to the power generation portion of the plant, is a crucial choice as well. TerraPower uses liquid sodium, Kairos uses molten fluoride salt, and X-energy uses helium gas. Different coolants can have advantages such as an increased efficiency of heat transfer, or eliminating the need for pressurized vessels.

The designs also incorporate safety features that don’t require human intervention to kick in, helping to ensure the reactor can shut down safely in an emergency. They harness simple physics, for example, relying on gravity, pressure differences or the natural convection of liquid coolant, to cool the core.

What’s next?

The concept of small modular reactors has been around for many years, but previous attempts haven’t panned out. Even recent efforts have stumbled. The reactor company NuScale was set to produce the first commercial small modular reactors in the United States, as part of a project in Idaho, but the project was cancelled in 2023 after costs ballooned.

Now, with big tech companies throwing themselves into the mix, proponents are hopeful that small modular reactors will be getting off the ground soon. 

“You can see the momentum building,” Allen says. “It doesn’t mean you’re going to have a new commercial version this year, but it’s also way more stuff going on that feels real than we’ve seen in nuclear for a very long time.”