Presidential candidates are in the business of making big promises, and few of the Democratic contenders for the 2020 nomination have promised more than Andrew Yang. An entrepreneur turned politico, Yang has styled himself as the techie’s candidate. His platform is defined by its embrace of high-tech solutions for a variety of social problems and earned him endorsements from Silicon Valley heavyweights like Elon Musk, Sam Altman, and Jack Dorsey. He advocates for returning ownership of digital data to users, a universal basic income as a salve for automation-fueled unemployment, and geoengineering to reverse climate change.
Yet of all Yang’s futuristic policies, one in particular stands out for its uniqueness and specificity. To transition the United States from fossil fuels to green energy, Yang wants the government to invest $50 billion in the development of thorium molten-salt nuclear reactors—and he wants them on the grid by 2027.
“Nuclear isn’t a perfect solution, but it’s a solid solution for now,” Yang’s climate policy page reads. It calls out thorium molten-salt reactors in particular as “a technology we should invest in as a stopgap for any shortfalls we have in our renewable energy sources as we move to a future powered by renewable energy.”
Thorium molten-salt reactors were first invented 60 years ago, but Yang appears to be the first presidential candidate to campaign on their promise to make nuclear energy safer, cleaner, and cheaper. Like all molten-salt reactors, they eschew solid rods of uranium-235 in favor of a liquid fuel made of thorium and a small amount of uranium dissolved in a molten salt. This approach to nuclear energy reduces proliferation risk, produces minimal amounts of short-lived toxic waste, and resists nuclear meltdowns.
As in a conventional nuclear reactor, splitting the nuclei of a nuclear fuel—a process known as fission—produces heat, which gets used to turn a turbine to generate electricity. But the Cold War arms race meant the US was already in the business of enriching uranium for weapons, so nuclear reactors based on solid uranium took off while liquid reactors stalled. No country has built a commercial molten-salt reactor.
As a result, many practical questions remain about the best way to design a thorium liquid-fuel reactor. Foremost among them, says Lin-Wen Hu, director of research and irradiation services at MIT’s Nuclear Reactor Laboratory, is finding materials that can contain the corrosive molten salts. Furthermore, figuring out how to extract unwanted elements produced as thorium decays—such as protactinium-233—from the fuel remains a major technical challenge.
“There is still a lot of work to be done in terms of demonstrating molten-salt reactor technology, even for uranium-based reactors,” Hu says. “Molten-salt reactors need to be demonstrated with a uranium fuel cycle before that system can be used for a thorium fuel cycle. Moving toward a thorium fuel cycle has a lot of unknowns.”
Plenty of countries, most notably China, are investing heavily in molten-salt reactor research in general and thorium reactors in particular. Unlike the United States, China doesn’t have to overcome the inertia of a robust and entrenched nuclear industry with a 70-year history. The country is also believed to have large deposits of thorium within its borders, but comparatively little uranium. The incentives are aligned for China to aggressively pursue thorium molten-salt reactors, but experts say this isn’t the case in the US.
“The nuclear industry is conservative, and there’s a lot of momentum behind uranium,” says Leslie Dewan, a nuclear engineer and a founding principal at Nucleation Capital, which invests in advanced nuclear energy companies. “That makes it more difficult to shift course into thorium.”
It’s also not clear that thorium reactors are the best way to rapidly decarbonize American energy. If the US did decide to build new nuclear plants—far from a given—uranium would have a significant edge over thorium. Developing the infrastructure to process thorium fuel would take years, for example, making it hard to meet Yang’s 2027 deadline for an operational thorium reactor on the grid. Deploying new uranium-based nuclear reactors would likely happen much more rapidly and at a substantially lower cost.
The main advantage of thorium is that the waste has a half-life on the order of dozens, rather than thousands, of years. From a power-generation perspective, the better option for Yang and other Democratic candidates may be to invest in advanced uranium-based technologies. This includes molten-salt reactors, but also solid-fuel systems like next-generation fast reactors, which are safer and more efficient than previous nuclear reactor designs. In some designs, next-generation reactors can even use preexisting nuclear waste as fuel.
“One of my concerns with the Yang climate plan is I think he probably just Googled “advanced nuclear,” took a look at the top hits online, and ran with that,” says Kieran Dolan, a nuclear engineering graduate student at MIT’s Nuclear Reactor Lab. “If the goal is really carbon reduction and getting advanced nuclear reactors deployed, then I don’t think thorium is the way to go.”
Neither does Congress. Over the years, a handful of attempts to fund research into thorium reactors have fallen flat. But a new bill introduced to Congress earlier this year—the Nuclear Energy Leadership Act—calls for the demonstration of two advanced nuclear reactors by 2025 and up to five other reactor demonstrations by 2035. Thorium isn’t mentioned in the bill, but a thorium-based reactor could conceivably be one of the reactor designs explored.
“I think the demonstration program that Congress is outlining right now is a great way to do things,” says Everett Redmond, senior technical adviser for new reactor and advanced technology at the Nuclear Energy Institute. “I think it will help spur innovation and bring down risk for companies developing these technologies.”
Redmond believes Yang’s proposed nuclear subsidy—$50 billion over five years—would greatly expedite research and development on advanced nuclear reactors, but none of the experts I spoke with thought that focusing on thorium molten-salt reactors was the best use of this money. “If we want to make a substantial dent in fossil fuel energy production, we need to get advanced nuclear reactors on the grid as quickly as possible,” says Dewan. “That means putting a substantial focus on uranium reactors in addition to thorium reactors.”
But Yang is certainly correct about one thing—it’s time to ditch fossil fuels, and the faster the better.
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