What is deuterium-tritium fuel?

How it works

Deuterium and tritium are isotopes, or variants, of hydrogen. The U.S. Department of Energy explains that every hydrogen nucleus has one proton. Deuterium also has one neutron. Tritium has two.

When the two fuse, they form helium and an energetic neutron. The department says those neutrons could be the basis for generating energy in future fusion power plants. It says the fuel reaches fusion conditions at lower temperatures than other elements. It also releases more energy than other fusion reactions.

"Lower" is relative. ITER puts the temperature of its own plasma at 150 million degrees Celsius. It says other fuels would need even more heat.

Very little fuel is involved. ITER says less than 1 gram is in its vacuum vessel at any one moment.

Where the fuel comes from

The two halves of the mix are very different to obtain:

• Deuterium is common. About 1 in every 6,500 hydrogen atoms in seawater is deuterium, the department says. ITER says it can be distilled from all forms of water.
• Tritium is rare in nature. It is radioactive, with a half-life of 12 years. ITER puts the global inventory at around 20 kilograms.

Future plants are expected to make their own tritium, a process called breeding. Neutrons escaping the plasma would meet lithium in the wall around it and produce tritium. The department says scientists are still researching how to breed tritium fast enough for a plant to supply itself.

Where things stand in 2026

Few machines have run on the mix. EUROfusion said in February 2024 that the JET tokamak in the United Kingdom was unique among tokamaks of the day in being able to use it. JET's final deuterium-tritium campaign set a record of 69.26 megajoules in a single pulse. That came from 0.21 milligrams of fuel. JET ended scientific operations at the end of 2023.

ITER, the international tokamak being assembled in France, plans to start with hydrogen and deuterium plasmas. Its timeline, as read on October 8, 2026, lists the start of research operation in 2034. Deuterium-tritium operation follows in 2039.

The mix has a drawback. Its energetic neutrons can damage structural materials. The department says scientists are also interested in reactions that avoid this, such as deuterium with helium-3. Those occur at higher temperatures.