Scientists

Nuclear fusion has seen some exciting advances, and the promise of clean, efficient energy does seem to be creeping closer to reality. But skeptics point to practical issues we may not be trying hard enough to solve—issues that will inevitably weigh down our reactors when they finally arrive.

A new proposal by Terence Tarnowsky, a nuclear physicist at Los Alamos National Laboratory, focuses on one key part of the problem: finding a supply of tritium, a fundamental ingredient for fusion. Tarnowsky, who will present his roadmap next week at the ACS Fall 2025 conference, suggests tapping into the thousands of tons of nuclear waste, including spent reactor fuel, using the sleeping atoms within to support tritium production. With the right adjustments to an accelerator-like apparatus, this strategy could reliably create a self-sufficient source of the precious isotope.

In a successful fusion reactor, tritium and deuterium—two lightweight hydrogen isotopes—fuse and release a gigantic load of energy in the process. By contrast, current nuclear plants run on fission, or the splitting of heavy atoms such as uranium, which also generates a hefty amount of power but produces long-lived radioactive byproducts. This waste material just “[sits] around the country,” presumably for a million years, and costs hundreds of millions of dollars each year to manage, Tarnowsky explained to Gizmodo during a video call. 

Meanwhile, the promise of fusion is shadowed by an inevitable shortage of tritium, an extremely rare and unstable hydrogen isotope. “There are only tens of kilograms [of tritium]—both natural and artificial—on the entire planet,” Tarnowsky said. And it doesn’t help that nuclear experiments worldwide are burning through those tiny supplies at an alarming rate. “So, where is this tritium supposed to come from?”

Breeding tritium in labs is a viable option, but again, there’s a very good reason we haven’t found the perfect recipe; it’s a “tricky fuel to deal with,” Tarnowsky said. 

“If you breed tritium now, it’s not like you can stash it in a container for 30 years from now, because it decays to helium-3 very quickly,” he explained. “And it also has the chemistry of hydrogen. Hydrogen likes to get out of things; it likes to get stuck in walls. So it’s a hard thing to deal with.” For context, the half-life of tritium is 12.3 years, meaning it decays to half of its original amount in that time.

Tarnowsky’s proposal combines previous theories with recent technological advancements. Simply, the idea is to employ a particle accelerator to trigger the decay of uranium and plutonium atoms inside nuclear waste, resulting in a series of neutron bursts and other nuclear transitions that would eventually produce tritium atoms. The waste would be covered with molten lithium salt to shield the process from overexposure to harmful radiation, according to Tarnowsky. 

With the right design, Tarnowsky surmises this method could “produce more than 10 times as much tritium as a fusion reactor at the same thermal power,” as noted in the press release. That said, he admits that this roadmap would require bold commitments from both the public and private sectors. 

Fusion economy is irreversible in some ways, Tarnowsky said. It’s certainly not something where one “can flip a switch and have a backup system running if something goes terribly wrong with tritium breeding,” Tarnowsky said. “You need to plan ahead by a very long time frame.”

But the longer we wait, the more we’re essentially digging ourselves into a hole, he said. “Every year we continue to operate our nuclear power plants—in a very safe manner!—we also make more spent fuel every year, [which] increases about 2,000 metric tons per year. So the liabilities are getting worse every year.”

All that said, Tarnowsky remains hopeful for the future of nuclear fusion—and, really, completing our transition toward clean energy. 

“I’d say, you know, 10 years ago, this kind of technology being proposed in this space would not have received this much interest; people were wary about nuclear power plants,” he said. “And then they went to burn dirty coal. Well, what are you going to do? But we’re having this conversation now, and people aren’t just reacting with fear.”

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