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

To feed artificial intelligence’s voracious appetite for energy, tech companies are turning to small nuclear reactors.

Last week, Google and Amazon announced deals with companies that are developing small modular reactors. These reactors would produce less power than current reactors, and many models include different types of fuel or coolant, 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 number 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 energy with the need for clean energy and the evolving availability of these models, you get a huge increase in interest,” says nuclear engineer Kathryn Huff of the University of Illinois Urbana-Champaign.

Meanwhile, the US government has supported the development of small modular reactors, further fueling interest.

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

What are small modular reactors?

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

Traditional nuclear plants require massive upfront investment, an obstacle that has stalled the construction of new reactors in the United States for decades. The first newly built reactors built at the country in 30 years — two in Waynesboro, Ga., to fire up in 2023 and 2024 — cost about $30 billion. Construction was years behind schedule and billions over budget.

By turning to smaller reactors, companies and policymakers aim to boost the spread of nuclear power, which is considered a reliable source of energy without emitting greenhouse gases.

Plus, since smaller reactors produce less power, less waste heat must 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 off-site in a factory and ship them where they need to go, rather than custom-build them from raw materials locally. “The more you can build these reactors like airplanes rather than airports, the cheaper it will be overall.”

What is driving the 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 power shifts. “In the last 10 years, it’s been a pretty steady and growing support, and I think that’s a big deal,” says nuclear engineer Todd Allen of the University of Michigan. Nuclear power 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 the bad guys of climate change (SN: 12/11/23). Google announced on October 14 that it would buy power from small modular reactors to be built by Kairos Power, which aims to have reactors up and running in the 2030s. And on October 16, Amazon announced an investment in the company X-energy and agreements with utilities in Virginia and Washington state to build small modular reactors.

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

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

Traditional nuclear plants still play a role for the foreseeable future. On Sept. 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 to operate (SN: 4/7/79))

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

How does the technology differ from current reactors?

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

Uranium used in reactors is enriched to include more of the corresponding 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 to 20 percent U-235, known as highly enriched uranium, or HALEU (SN: 7/3/24). The fuel allows small modular reactors to operate more efficiently than a conventionally fueled reactor. The United States does not produce HALEU commercially in significant quantities, but efforts are beginning to increase, in anticipation of the need.

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

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

The models also include safety features that do not require human intervention to enter, helping to ensure safe shutdown of the reactor in the event of an emergency. They use simple physics, for example, relying on gravity, pressure changes 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 have not panned out. Even the latest efforts have stalled. 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 canceled in 2023 as costs rose.

Now, with big tech companies getting into the mix, proponents hope small modular reactors will soon be up and running.

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