Nuclear Fusion Already Has a Fuel Shortage

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Nuclear fusion has run into a supply deficit of tritium, the primary fuel source for the most renowned experimental reactors.

ITER, in the south of France, is nearing completion. The International Thermonuclear Experimental Reactor will be the largest device of its kind ever built and the flag-bearer for nuclear fusion when it is fully operational in 2035.

Two types of hydrogen, deuterium and tritium, will be smashed together inside a donut-shaped reaction chamber called a tokamak until they fuse in a roiling plasma hotter than the surface of the sun, releasing enough clean energy to power tens of thousands of homes—a limitless source of electricity straight from science fiction.

That is, at least, the plan. The issue, which is the elephant in a room full of potential elephants, is that by the time ITER is ready, there may not be enough fuel to run it.

For its experiments, ITER, like many of the most well-known experimental nuclear fusion reactors, relies on a constant supply of both deuterium and tritium. Although deuterium may be recovered from seawater, tritium, a radioactive hydrogen isotope, is extremely rare.

Tritium levels in the atmosphere peaked in the 1960s, before the prohibition on nuclear weapons testing, and according to the most recent estimations, there is currently less than 20 kg (44 pounds) of tritium on Earth. Our finest sources of tritium to power ITER and other experimental fusion reactors are slowly depleting as the project grinds on, years behind time and billions over budget.

Tritium for fusion experiments like ITER and the smaller JET tokamak in the UK currently comes from a very specialized sort of nuclear fission reactor known as a heavy-water moderated reactor. However, many of these reactors are nearing the end of their useful lives, with only approximately 30 remaining in operation around the world—20 in Canada, four in South Korea, and two in Romania, each producing roughly 100 grams of tritium each year. (India aims to construct more, but its tritium is unlikely to be made available to fusion researchers.)

However, this is not a long-term feasible solution—the entire goal of nuclear fusion is to provide a cleaner and safer alternative to traditional nuclear fission power. "It would be a farce to utilize dirty fission reactors to fuel 'clean' fusion reactors," says Ernesto Mazzucato, a retired physicist who, despite spending much of his working life investigating tokamaks, has been an outspoken critic of ITER and nuclear fusion in general.

The second issue with tritium is that it is unstable. It has a half-life of 12.3 years, which means that half of the tritium available now will have decayed into helium-3 by the time ITER is ready to commence deuterium-tritium operations (in around 12.3 years). After ITER is turned on, and several more deuterium-tritium (D-T) successors are planned, the situation will only get worse.

These two forces have aided in the transformation of tritium from an undesired byproduct of nuclear fission that had to be carefully disposed of into the most expensive substance on the planet, according to some estimates. It costs $30,000 each gram, and operational fusion reactors will require up to 200 kg per year. To make matters worse, nuclear weapons programs want tritium because it helps make bombs more powerful—despite the fact that military tend to generate it themselves since Canada, which produces the majority of the world's tritium, refuses to sell it for non-peaceful purposes.

Paul Rutherford, a researcher at Princeton's Plasma Physics Laboratory, predicted this problem in 1999 and described the "tritium window," a sweet spot where tritium supplies would peak before dropping when heavy-water-moderated reactors were turned off. We're at that sweet spot right now, but ITER isn't ready to take advantage of it because it's about a decade behind schedule. "Everything would have worked out great if ITER had been producing deuterium-tritium plasma like we planned around three years ago," says Scott Willms, ITER's fuel cycle division leader. "Right now, we're approaching the peak of this tritium window."

Scientists have known about this potential stumbling block for decades, and they've devised a clever solution: using nuclear fusion reactors to "breed" tritium, allowing them to replenish their own fuel while burning it. Breeder technology aims to work by wrapping a "blanket" of lithium-6 around the fusion reactor.

When a neutron leaves the reactor and collides with a lithium-6 molecule, tritium should be produced, which may then be recovered and returned to the process. According to Stuart White, a spokesperson for the UK Atomic Energy Authority, which hosts the JET fusion project, "Calculations suggest that a suitably designed breeding blanket would be capable of providing enough tritium for the power plant to be self-sufficient in fuel, with a little extra to start up new power plants."

Tritium breeding was supposed to be tested as part of ITER, but it was abruptly cancelled as prices rose from $6 billion to more than $25 billion. At ITER, Willms is in charge of smaller-scale tests. ITER will use suitcase-sized samples of variously presented lithium injected into "ports" around the tokamak instead of a whole blanket of lithium enclosing the fusion reaction: ceramic pebble beds, liquid lithium, and lead lithium.

Even Willms acknowledges that this technology is far from ready for deployment, and that a full-scale test of tritium breeding will have to wait until the next generation of reactors, which some feel is already too late. "After 2035, we'll have to build a new machine that will take another 20 or 30 years to test a critical task like how to manufacture tritium," Mazzucato says. "How will we be able to block and stop global warming using fusion reactors if we won't be ready until the end of this century?"

There are alternative ways to make tritium, such as actively injecting breeding material into nuclear fission reactors or shooting neutrons at helium-3 with a linear accelerator, but these methods are too expensive to be utilized in large amounts, thus they will likely remain a nuclear weapons reserve. In an ideal world, Willms argues, there would be a more ambitious program developing breeding technology alongside ITER, so that when ITER perfects the fusion reactor, there is still a fuel source to power it. He explains, "We don't want to build the car and then run out of gas."

The tritium problem is driving doubts about ITER and other D-T fusion projects. These two elements were chosen because they fuse at a low temperature, making them the easiest to work with in the early days of fusion. Everything else felt impossible at the time.

Some businesses are now looking into alternatives, using AI-controlled magnets to help contain the fusion reaction and breakthroughs in materials science. TAE Technologies, based in California, is working on a hydrogen-and-boron fusion reactor that it claims will be a cleaner and more practical alternative to D-T fusion.

By 2025, it hopes to achieve a net energy gain, in which a fusion reaction produces more energy than it consumes. Boron can be harvested by the metric ton from seawater, with the added bonus of not irradiating the equipment like D-T fusion does. It's a more commercially viable way to scalable fusion power, according to TAE Technologies CEO Michl Binderbauer.

Despite the possible supply concerns for ITER's core fuel, the mainstream fusion community remains optimistic. "Fusion is really tough," Willms argues, "and anything other than deuterium-tritium will be 100 times more difficult." "Perhaps we can talk about something else in a century."