The ITER fusion megareactor is expected to consume most of the world’s tritium fuel, which could leave the field of fusion energy with an empty tank.
In 2020, Canadian Nuclear Laboratories delivered five steel drums, lined with cork to absorb shocks, to the Joint European Torus , 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.
Fusion advocates often boast that the fuel for their reactors will be cheap and plentiful. That is certainly true for deuterium: Roughly one in every 5000 hydrogen atoms in the oceans is deuterium, and it sells for about $13 per gram. But tritium, with a half-life of 12.3 years, exists naturally only in trace amounts in the upper atmosphere, the product of cosmic ray bombardment. Nuclear reactors also produce tiny amounts, but few harvest it.
Scarce tritium is not the only challenge fusion faces; the field must also learn to deal with fitful operations, turbulent bursts of plasma, and neutron damage . But for Daniel Jassby, a plasma physicist retired from Princeton Plasma Physics Laboratory and a known critic of D-T fusion energy, the tritium issue looms large. It could be fatal for the entire enterprise, he says. “This makes deuterium-tritium fusion reactors impossible.”reactors, D-T fusion would be an unattainable dream.
Once ITER finishes work in the 2050s, 5 kilograms or less of tritium will remain, according to the ITER projections. In a worst-case scenario, “it would appear that there is insufficient tritium to satisfy the fusion demand after ITER,” concedes Gianfranco Federici, head of fusion technology at the EuroFusion research agency.
DEMO’s designers are working on ways to reduce its startup needs. “We need to have a low tritium [starting] inventory,” says Christian Day of the Karlsruhe Institute of Technology, project leader in the design of DEMO’s fuel cycle. “If you need 20 kilograms to fill it, that’s a problem.” The tritium can be extracted continuously or during scheduled shutdowns, depending on whether the lithium is in liquid or solid form, but the breeding must be relentless. The breeding blankets also have a second job: absorbing gigawatts of power from the neutrons and turning it into heat. Pipes carrying water or pressurized helium through the hot blankets will pick up the heat and produce steam that drives electricity-producing turbines.
Two private fusion efforts have decided to simply forgo tritium fuel. TAE Technologies, a California startup, plans to use plain hydrogen and boron, whereas Washington state startup Helion will fuse deuterium and helium-3, a rare helium isotope. These reactions require higher temperatures than D-T, but the companies think that’s a price worth paying to avoid tritium hassles. “Our company’s existence owes itself to the fact that tritium is scarce and a nuisance,” says TAE CEO Michl Binderbauer.
The U.S. Department of Energy , for example, relies on commercial reactors—Watts Bar Units 1 and 2, operated by the Tennessee Valley Authority—in which lithium control rods have replaced some of the boron ones. The rods are occasionally removed and processed to extract tritium. DOE supplied PPPL with tritium in the 1980s and ’90s when the lab had a D-T burning reactor. But Federici doesn’t think the agency, or militaries around the world, will get into the business of selling the isotope.
Some of fusion’s fitfulness is innate to the design of doughnut-shaped tokamak reactors. The magnetic field that confines the ultrahot, energy-producing plasma is generated in part by the charged particles themselves, as they flow around the vessel. That plasma current in turn is induced by pulses of electrical current in a coil of wire in the doughnut’s hole, each lasting a few minutes at most. In between pulses the magnetic field ebbs, interrupting tokamak operations—and power delivery.
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