UK’s JET nuclear fusion reactor sets new world record for energy output

Inside the JET fusion reactor


Britain's 40-year-old fusion reactor reached a world record for energy production during its final operations before being permanently shut down, scientists have said.

The Joint European Torus (JET) in Oxfordshire began operating in 1983. When operating, it was temporarily the hottest point in the solar system, reaching 150 million °C.

The reactor's previous record was a reaction lasting 5 seconds in 2021, producing 59 megajoules of thermal energy. But in its final tests in late 2023, it surpassed that figure by sustaining a reaction for 5.2 seconds while achieving 69 megajoules of power, using just 0.2 milligrams of fuel.

This is equivalent to 12.5 megawatts of power, enough to power 12,000 homes, Mikhail Maslov of Britain's Atomic Energy Authority said at a press conference on February 8.

Today's nuclear power plants rely on fission reactions, where atoms are broken apart to release energy and smaller particles. Fusion works in reverse, bringing smaller particles together into larger atoms.

Fusion can create more energy without any of the radioactive waste created by fission, but we don't yet have a practical way to harness this process in a power plant.

JET forged deuterium and tritium atoms – two stable isotopes of hydrogen – together in a plasma to create helium, while releasing a large amount of energy. It's the same reaction that powers our sun. This was a type of fusion reactor known as a tokamak, which contains donut-shaped plasma using rings of electromagnets.

Scientists conducted the latest experiments with deuterium-tritium fuel at JET in October last year and further experiments continued until December. But the machine is now permanently shut down and will be decommissioned for the next 16 years.

Juan Matthew at the University of Manchester, UK, says JET will reveal many secrets as it is dismantled, such as how the reactor's cladding deteriorated upon contact with plasma and where the precious tritium – worth around £30,000 a gram – has become embedded in the machinery and can be recovered. This will be vital information for future research and commercial reactors.

“It’s great that it came out with a bit of a flourish,” Matthews says. “His story is noble. It's served its time and they're going to extract a little more information from it during its decommissioning period as well. So there is nothing to be sad about; it’s something that should be celebrated.

A larger, more modern replacement for JET, the International Thermonuclear Experimental Reactor (ITER) in France, is nearing completion with its first experiments expected to start in 2025.

Tim Luce, deputy construction project director of ITER, said at the press conference that ITER would increase energy production to 500 megawatts, or even 700.

“That’s what I usually call power plant scale,” he said. “They are at the lower end of what you would need for a power generation facility. Additionally, we need to extend the delay to at least 300 seconds for high fusion power and gain, but perhaps up to an hour in terms of power output. So what JET has done is exactly a scaled-down model of what we need to do within the ITER project.

Another reactor using the same design, the Korea Superconducting Tokamak Advanced Research (KSTAR) device, recently managed to sustain a reaction for 30 seconds at temperatures above 100 million °C.

There are other approaches to creating a working fusion reactor that are also being studied around the world, such as the National Ignition Facility at the Lawrence Livermore National Laboratory in California. This bombarded fuel capsules with extremely powerful lasers, a process called inertial confinement fusion, and managed to release almost twice the energy injected into them.

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