OUT OF GAS? A shortage of tritium fuel may leave fusion energy with an empty tank.

Throughout the decades of fusion research, plasma physicists have been single-minded about reaching the breakeven point and producing excess energy. They viewed other issues, such as acquiring enough tritium, just “trivial” engineering. But as reactors approach breakeven, nuclear engineers say it’s time to start to worry about engineering details that are far from trivial. “Leaving [them] until later would be hugely mistaken.”


In 2020, Canadian Nuclear Laboratories delivered five steel drums, lined with cork to absorb shocks, to the Joint European Torus (JET), a large fusion reactor in the United Kingdom. Inside each drum was a steel cylinder the size of a Coke can, holding a wisp of hydrogen gas—just 10 grams of it, or the weight of a couple sheets of paper.

This wasn’t ordinary hydrogen but its rare radioactive isotope tritium, in which two neutrons and a proton cling together in the nucleus. At $30,000 per gram, it’s almost as precious as a diamond, but for fusion researchers the price is worth paying. When tritium is combined at high temperatures with its sibling deuterium, the two gases can burn like the Sun. The reaction could provide abundant clean energy—just as soon as fusion scientists figure out how to efficiently spark it.

Last year, the Canadian tritium fueled an experiment at JET showing fusion research is approaching an important threshold: producing more energy than goes into the reactions. By getting to one-third of this breakeven point, JET offered reassurance that ITER, a similar reactor twice the size of JET under construction in France, will bust past breakeven when it begins deuterium and tritium (D-T) burns sometime next decade. “What we found matches predictions,” says Fernanda Rimini, JET’s plasma operations expert.

But that achievement could be a Pyrrhic victory, fusion scientists are realizing. ITER is expected to consume most of the world’s tritium, leaving little for reactors that come after.

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