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Fusion power is coming back into fashion The Economist – 22.03.23

This time it might even work.


On January 12th Oxfordshire County Council, in England, gave the go-ahead for a new building near the village of Culham. The applicant, General Fusion, is a Canadian firm, and the edifice will house its Fusion Demonstration Program, a seven-tenths-scale prototype of a commercial nuclear-fusion reactor. The firm picked Culham because it is the site of JET, the Joint European Torus, an experimental fusion reactor opened in 1983 by a consortium of governments. That means there is plenty of local talent to be recruited.


General Fusion is not alone. On February 10th Tokamak Energy, a British firm, announced plans for a quarter-scale prototype, the ST80, also at Culham. And in 2024 they will be joined there by Machine 4, a pre-commercial demonstrator from another British outfit, First Light Fusion.


Meanwhile, across the ocean in Massachusetts, Commonwealth Fusion Systems is already building, in Devens, a town west of Boston, a half-scale prototype called SPARC. On the other side of America, in Everett, Washington, Helion Energy is likewise constructing a prototype called Polaris. And in Foothill Ranch, a suburb of Los Angeles, TAE Technologies is similarly working on a machine it calls Copernicus.


These six firms, and 36 others identified by the Fusion Industries Association (FIA), a trade body for this incipient sector, are hoping to ride the green-energy wave to a carbon-free future. They think they can succeed, where others failed, in taking fusion from the lab to the grid—and do so with machines far smaller and cheaper than the latest intergovernmental behemoth, ITER, now being built in the south of France at a cost estimated by America’s energy department to be $65bn. In some cases that optimism is based on the use of technologies and materials not available in the past; in others, on simpler designs.


Many of those on the FIA’s rapidly growing list are tiddlers. But General Fusion, Tokamak, Commonwealth, Helion and TAE have all had investments in excess of $250m. TAE, indeed, has received $1.2bn and Commonwealth $2bn. First Light is getting by on about $100m. But it uses a simpler approach than the others (“fewer screws”, as Bart Markus, its chairman, puts it), so has less immediate need for cash.


All these firms have similar timetables. They are, or shortly will be, building what they hope are penultimate prototypes. Using these they plan, during the mid-to-late 2020s, to iron out remaining kinks in their processes. The machines after that, all agree, will be proper, if experimental, power stations—mostly rated between 200MW and 400MW—able to supply electricity to the grid. For most firms the aspiration is to have these ready in the early 2030s.


Un peu d’histoire


The idea of harnessing the process that powers the sun goes back almost as far as the discovery, in the 1920s and 1930s, of what that process is—namely the fusion of protons, the nuclei of hydrogen atoms, to form helium nuclei (4He), also known as alpha particles. This reaction yields something less than the sum of its parts, for an alpha particle is lighter than four free protons. But the missing mass has not disappeared; it has merely been transformed. As per Einstein’s equation, E=mc2, it has been converted into energy, in the form of heat.


This sounded technologically promising. But it was soon apparent that doing it the way the sun does is a non-starter.


Persuading nuclei to fuse requires heat, pressure or both. The pressure reduces the space between the nuclei, encouraging them to meet. The heat keeps them travelling fast enough that when they do meet, they can overcome their mutual electrostatic repulsion, known as the Coulomb barrier, and thus allow a phenomenon called the strong nuclear force, which works only at short range, to take over. The strong force holds protons and neutrons together to form nuclei, so once the Coulomb barrier is breached, a new and larger nucleus quickly forms.


The temperature at which solar fusion occurs, though high (15.5m°C), is well within engineers’ reach. Experimental reactors can manage 100m°C and there are hopes to go higher still. But the pressure (250bn atmospheres) eludes them. Moreover, solar fusion’s raw material is recalcitrant. The first step on the journey to helium—fusing two individual protons together to form a heavy isotope of hydrogen called deuterium (a proton and a neutron)—is reckoned to take, on average, 9bn years.


What engineers propose is thus a simulacrum of the solar reaction. The usual approach—that taken by General Fusion, Tokamak Energy, Commonwealth Fusion and First Light, as well as government projects like JET and ITER—is to start with deuterium and fuse it with a yet-heavier (and radioactive) form of hydrogen called tritium (a proton and two neutrons) to form 4He and a neutron. (Fusing deuterium nuclei directly, though sometimes done on test runs, is only a thousandth as efficient.)


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This article appeared in the Science & technology section of the print edition under the headline "The other nuclear energy"

Credit: Tokamak Energy


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