American scientists have announced a historic breakthrough in the field of nuclear fusion. What is it?
Eva Deschamps / December 14, 2022
For many, nuclear fusion is the energy of the future. Its advantages are numerous: it generates no CO2, less radioactive waste, and presents no risk of nuclear accidents.
Here is an update on how it works, what projects are underway and when they could be completed.
Nuclear fusion differs from fission, the technique currently used in nuclear power plants, which involves breaking the bonds of heavy atomic nuclei.
Fusion is the opposite process: two light atoms (hydrogen) are fused to create a heavy one (helium), which releases energy.
This is the process that is at work in stars, including our Sun.
"Controlling the energy source of stars is the greatest technological challenge ever undertaken by mankind," wrote physicist Arthur Turrell, author of The Star Builders, on Twitter.
Fusion is only possible by heating matter to extremely high temperatures (of the order of 150 million degrees).
"So we must find ways to isolate this extremely hot material from anything that could cool it. This is the problem of containment," Erik Lefebvre, project leader at the French Atomic Energy Commission (CEA), explained to AFP.
The first method is the fusion by magnetic confinement. In a huge reactor, light hydrogen atoms (deuterium and tritium) are heated. The material is then in the state of plasma, a very low density gas. It is controlled by a magnetic field, obtained with magnets.
This is the method that will be used for the international ITER project, currently under construction in France, and the one used by the JET (Joint European Torus) near Oxford.
A second method is inertial confinement. Here, very high energy lasers are sent inside a cylinder the size of a thimble, containing the hydrogen.
This is the technique used by the French Megajoule Laser (LMJ), or the most advanced project in this field, the American National Ignition Facility (NIF). It is in the latter that the historic experiment was carried out that allowed for the first time a net gain in energy.
The goal of the laboratories using lasers was until now more to demonstrate the physical principle, while the first method seeks to reproduce a configuration close to a future fusion reactor.
There is still a "very long way to go" before "a demonstration on an industrial scale that is commercially viable," warns Érik Lefebvre. According to him, such projects will take another 20 or 30 years to be completed.
Probably "decades" (but less than five), agreed on Tuesday Kim Budil, director of the Lawrence Livermore National Laboratory, on which the American NIF depends.
Now that a net energy gain has been achieved with lasers, "we need to figure out how to make it simpler," she said.
Many technological improvements are still needed: the amount of energy produced will have to be increased, and the operation will have to be repeatable multiple times per minute.
Unlike fission, fusion does not involve any risk of nuclear accident. "If a few lasers are missing and they don't go off at the right time, or if the confinement of the plasma by the magnetic field (...) is not perfect," the reaction will simply stop, explains Érik Lefebvre.
Moreover, nuclear fusion produces less radioactive waste than current power plants.
Above all, it does not generate greenhouse gases.
"It is an energy source that is totally decarbonized, generates very little waste, and is intrinsically extremely safe," summarizes Lefebvre. This makes it "a future solution for energy problems on a global scale ».
However, due to its still early stage of development, it does not represent an immediate solution to the climate crisis and the need for a rapid transition from fossil fuels.