In the scramble to stave off climate change, scientists are exploring every possible source of energy that does not rely on fossil fuels. Fusion is one such resource. How close are we to being able to rely on this technology?
In December 2021, the Joint European Torus (JET) reactor in Oxfordshire, UK, produced 59 megajoules of energy during a five-second period. This burst of energy – enough to boil about 60 kettles of water – was the “absolute maximum” JET could create, according to the project’s lead scientist.
One month later, China’s EAST (Experimental Advanced Superconducting Tokamak) sustained a fusion reaction at 158 million degrees Fahrenheit for more than 17 minutes – ten times longer than its prior record of 101 seconds. That earlier experiment had operated at an even higher temperature of 216 million degrees Fahrenheit.
Temperatures many times hotter than the core of the sun’s 27 million degrees Fahrenheit are needed to create fusion here on Earth given our planet’s smaller mass and lower gravity. More than 160 fusion experimental facilities have been built globally, yet none has succeeded in producing this extreme heat for more than very brief periods.
Achieving a net energy gain from nuclear fusion is another unmet challenge. The UK’s JET experiment last December consumed three times more energy than it produced. The U.S. Department of Energy’s National Ignition Facility performed slightly better in August 2021, with an energy output equaling 70 percent of energy expended, but for a period that lasted only 100 trillionths of a second. No fusion experiment to date has reached Q equals 1, the threshold at which energy output matches energy input.
For fusion to be a practical solution to our energy woes, several multiples of Q will have to be achieved in a continuously operating plant, and at a price that can hold its own in the electric power marketplace.
No ‘silver bullet’ in a race against the climate clock
In Massachusetts, the founders of an MIT spinoff called Commonwealth Fusion Systems (CFS) claim they are developing a fast-track platform for addressing some of these conundrums. Their proving ground will be a test facility about 40 miles west of Boston, adjacent to the Fort Devens army base.
On a blustery morning this past December, CFS invited members of the Massachusetts environmental community, including the author of this piece, to tour its facility, now under construction. With cranes and earthmovers rumbling in the background, Kristen Cullen, public affairs director at CFS, stressed the timeliness of her firm’s ambition: “We are in a race, a race against the clock.”
Cullen and her colleagues are driven in part by the looming specter of climate change. They look to fusion as an energy resource that can work in tandem with renewable technologies like wind and solar to meet growing global energy demand while phasing out carbon-intensive industries like coal, oil and gas. “We all know that what we’re doing is not a silver bullet,” said Cullen. “It’s not the one and only solution that’s going to save the planet, but it’s part of the mix.”
Also driving CFS is a determination to outcompete China and other nations already well-advanced in their fusion experiments. An early CFS supporter who joined that December tour stated it bluntly: “There’s a trillion-dollar export market for whoever gets there first.” Having just landed $1.8 billion in financing from Bill Gates, Google, a major university endowment, and others, CFS is readying itself to enter this race.
Dozens of hard-hatted workers were busy assembling massive bulwarks of steel-reinforced concrete as the group approached the building that will house the CFS tokamak, which takes its name from early Soviet fusion experiments dating back to the late 1960s. Within the tokamak is a doughnut-shaped vacuum vessel specially designed to generate nuclear fusion and contain the resulting superheated plasma.
To create fusion, deuterium and tritium – two heavy isotopes of hydrogen – will be blasted by high-energy radio waves, yielding helium and also neutrons loaded with kinetic energy. High-temperature superconducting magnets specially designed by MIT’s Plasma Science and Fusion Center will then be used to suspend the energy-rich plasma within the vacuum vessel, isolating it from direct physical contact with the vessel’s walls and other reactor machinery. The Plasma Science and Fusion Center’s director Dennis Whyte describes this arrangement as a “magnetic cage,” with MIT’s high-temperature superconducting magnets replacing the much larger and heavier magnets used in other fusion experiments.
Tyler Ellis, a nuclear physicist and CFS advisor, explains the test facility’s initial goal: achieving an energy balance of Q greater than 1 by 2025. Once that threshold has been demonstrated, CFS will set about proving that it is possible to build a fusion-based power plant about 40 times smaller than facilities relying on low-temperature superconducting magnets, like the International Thermonuclear Experimental Reactor (ITER) in southern France.
A 35-nation partnership, ITER has long been the iconic focus for fusion development. Its scientists had expected to create their first fusion plasma by 2025, but the consortium’s management recently acknowledged that, given challenges posed by Covid and other setbacks, this milestone is out of reach. Completion of a fully functioning power plant, still officially projected for 2035, is also likely to be delayed by several years.
CFS may be able to address development challenges more nimbly and at lower cost because of its innovative magnet technology, but the company will face many of the same hurdles that have stymied other fusion initiatives. The CFS magnets have yet to be tested in an operating tokamak, making it impossible to predict how many years of exacting experimentation will be needed to overcome disruptions and instabilities that may compromise the integrity of fusion equipment and operations.
Unanswered questions about radioactivity
Sustaining a stable fusion reaction is just one step on the path to fusion-based electricity. To produce electric power, some of the plasma’s extraordinary heat must be drawn off safely to create the steam that will turn electric turbines. As Ellis describes it, neutrons escaping from the tokamak’s magnetic cage will bounce through the vacuum vessel’s walls. Encircling those walls, an encased layer of molten lithium salt will capture the neutrons’ kinetic energy, making it available as heat for steam generation. Whyte calls this the reactor’s “thermal blanket.”
Plant operators will also have to find safe ways to manage radioactive tritium. Some tritium fuel accumulates in the reactor vessel as residue from incomplete fusion; some is produced when neutrons are absorbed by lithium in the thermal blanket. In both instances, Ellis says the tritium can be purified for reuse as a fusion fuel. He and his colleagues insist that tritium in the CFS tokamak will be present in very small amounts – equivalent to the radioactivity in some forms of medical waste. It also has a relatively short half-life – 12.3 years compared to the hundreds of millions of years it takes uranium wastes from fission-based nuclear power to decay.
Though much less enduring than uranium, radioactive tritium may pose a greater hazard to workers and the environment than Ellis anticipates. Evidence of this concern was made apparent on January 25, when France’s Nuclear Safety Authority cited inadequate mapping of potential worker radiation exposure as one of three reasons for issuing a stop order on construction at the giant ITER fusion facility.
Once a fusion plant goes into regular operation, radioactivity will build up in the reactor and surrounding building. ITER’s Director General Bernard Bigot says that this will require workers to remain outside the building while the plant is in operation. Over time, irradiated reactor vessel panels and other hardware at fusion plants will need to be replaced and safely disposed of – a painstaking process demanding long, costly periods of reactor downtime while robotics are deployed to minimize worker exposure.
For decades now, we have heard the familiar trope that nuclear fusion is 30 years away from becoming a “near-limitless clean power source.” Dedicated innovators backed by forward-looking investors may brighten the prospects for fusion power, but it’s too soon to say whether fusion will someday be deemed safe and affordable.
Meanwhile, our deteriorating global climate cannot wait for a clear answer. Barring a dramatic breakthrough in fusion’s feasibility, well-proven alternatives to fossil fuels – solar, wind , geothermal, improved energy storage, efficiency investments, and others – will remain our safest and surest pathways to a lower-carbon future.
Philip Warburg, an environmental lawyer and former president of the Conservation Law Foundation, is a Senior Fellow at Boston University’s Institute for Sustainable Energy. On twitter: @pwarburg.