In 2023, Georgia’s Vogtle brought online the nation’s first new nuclear reactor built from scratch in more than three decades. Last year, a second new reactor turned on, transforming Vogtle into the nation’s second-largest power station.

Now, one of Vogtle’s legacy reactors quietly marked another major nuclear milestone that experts say could shake up the rules for the industry. 

Engineers loaded the old reactor with a new type of uranium fuel enriched above the traditional threshold and designed to withstand all kinds of accidents, last longer without refueling, and generate less radioactive waste. In April, the reactor powered up to full capacity, becoming the first commercial reactor in the U.S. to run on next-generation fuel. 

It’s the first time in U.S. history a commercial reactor is running on fuel enriched above 5%. That may not sound like much, but many industry analysts recognize the redesigned uranium fuel as a monumental step change for the nuclear sector.

“This is enabling us to get more out of those existing reactors than in the past,” Jonathan Chavers, Southern’s director of nuclear fuel and analysis, told Fortune exclusively. “It’s a significant game changer for the industry.”

There’s a lot of excitement in the nuclear world now with the Trump administration promising to remove nuclear regulatory hurdles and new nuclear technologies ready to take hold, including small modular reactors that use coolants other than water. These are considered fourth-generation models in a world where most reactors in use are second or third gen. 

Asked whether the leap from traditional uranium fuel to the pellets Southern (ranked 161 in the Fortune 500) rolled out this spring represented the same jump in technology from third to fourth gen, Ken Petersen, the former president of the American Nuclear Society, laughed.

“This is like going from a Generation I to a Generation IV,” said Petersen, a retired fuel executive from Constellation, the nation’s largest nuclear utility. “It’s really breathtaking. We’re breaking barriers.”

What’s not clear is how widely adopted the new fuel could be in the short term with existing nuclear facilities other than Vogtle. Companies may not want to make the financial investment for older reactors.

Brett Rampal, a nuclear engineer and consultant who previously worked on core design at Westinghouse, called the new fuel program a “big waste of time”—for now. 

“As a guy who sold fuel to existing reactor operators, it didn’t matter what I was selling to my customer or utility. It didn’t matter what improvement to the fuel there was,” he said. “The bottom line they asked me is, ‘You’re going to sell this to me at the same price, right?’ Why would we sell you new and improved fuel for the same price? Then they’d say, ‘We’re not interested.’”

How it works

The nuclear fuel that goes into reactors is not the same uranium that comes out of the ground. Once mined, uranium ore is crushed, sorted and compacted into yellowcake, which is then converted into uranium hexafluoride through a chemical process. That grayish solid material is put through a centrifuge to enrich a small percentage of the uranium into uranium-235, the unstable isotope that can split to release energy in the form of heat. 

At the end of the enrichment process, gummy bear-sized pellets of fuel are loaded into fuel assemblies like PEZ candy in a dispenser and placed into a reactor that can spark the chain reaction called atom splitting, and the resulting heat is harnessed.

At that point, a nuclear power plant functions just like the coal-fired stations that came before it: the heat turns water into steam that spins turbines and generates electricity. 

Since the dawn of the nuclear industry in the U.S., the enrichment process has capped the amount of U-235 present in the fuel at 5%—an artificial industry threshold set decades ago and retained out of what experts said was a sense of inertia in an industry whose tight rules offered little room for innovation. All the atomic energy contained in the other 95% of the uranium that isn’t split contributes to the leftover radioactive waste at the end of the fuel cycle. 

In 2012, the year after the Fukushima disaster crushed public support for nuclear power, Congress established the Department of Energy’s accident-tolerant fuel program. At the time, Plant Vogtle was preparing to start construction on the first Westinghouse AP1000, a new generation of reactor with safety features that made a meltdown like the one in Japan almost impossible. The fuel program promised to make uranium pellets themselves that much safer. 

The pellets are “doped,” meaning the uranium blend in the nuggets of fuel is modified with materials such as chromium oxide and alumina to improve performance under high heat. 

In other words: all the highly radioactive materials that form during the fission process are better contained in the new fuel.

But the next breakthrough in Southern’s novel fuel is newer. The actual cladding in the fuel assemblies—the part that you load the candy into in a PEZ dispenser—is now coated in a zirconium alloy that can withstand more intense heat. 

“That helps the rod protect itself in a high-temperature environment,” Chavers said. “[Let’s] say a Fukushima-style event occurred at a nuclear reactor. The coating would protect the rod for an additional amount of time so we could get cooling into the core.” 

With those features in place, the reactor can run hotter, allowing it to burn up more U-235. That means the new fuel can be enriched higher—up to 8%. It may not sound like a lot, but the effect is nuclear reactors that must be refueled every 18 months can instead run for 24 months or longer without taking costly breaks to swap out the rods of uranium pellets. 

Still, of all the major commercial nuclear operators Fortune contacted to ask about Southern’s breakthrough, none indicated immediate plans to buy the new fuel. 

While the new fuel could be commercially manufactured relatively soon, commercial versions of the so-called cladding are likely at least a decade away, according to Southern.

Pacific Gas & Electric, the owner of California’s last nuclear plant Diablo Canyon, said it “remained focused on operating to 2030 with our current fuel design.” New Jersey-based PSEG declined to comment.

The Tennessee Valley authority said only that it “supports accident-tolerant fuels developments” and believes “Southern’s achievement is a good step towards bringing higher assay fuels to market.” Xcel Energy called the milestone “a significant achievement that will enhance safety and reliability,” but declined to say whether it would buy the fuel. 

On the other hand, Virginia’s Dominion Energy said it was “considering using [fuel] similar to what’s being piloted by Southern.” 

And, while Baltimore-based Constellation said it had “no current timeline for the large-scale use of newer fuels” in its reactors, the nuclear utility said, “We would deploy these newer fuels in our reactors once they make the transition from research and development to a commercial offering.”

New nuclear plants won’t come online anytime soon, so maximizing existing facilities is critical. “If you look at U.S. capacity factors, we’re higher than anybody else,” Petersen said. “We’re pushing up against those limits, and that’s why we need this additional enrichment.”