Andrew Yang, like many of the 2020 Democratic presidential hopefuls, has an ambitious plan to wean America off of fossil fuels. Unlike many of the other candidates, however, a key piece of his plan to address climate change involves harnessing nuclear power—in particular thorium. According to Yang, thorium is “superior to uranium on many levels.” But Yang isn’t alone; thorium boosters have been extolling its supposed virtues for years.
Do the claims about thorium actually hold up? The Bulletin reached out to Nicholas R. Brown, an associate professor in the department of Nuclear Engineering at the University of Tennessee, to examine five common claims about thorium and next-generation nuclear reactors. Brown’s responses are below.
Overall, although existing and new nuclear reactors may indeed be part of a long-term carbon-free energy mix in the United States, the public has good reason to be skeptical that thorium can or should play any role in the future.
Claim: Thorium reactors would be more economical than traditional uranium reactors, particularly because thorium is more abundant than uranium, has more energy potential than uranium, and doesn’t have to be enriched.
False. Although thorium is more abundant than uranium, the cost of uranium is a small fraction of the overall cost of nuclear energy. Nuclear energy economics are driven by the capital cost of the plant, and building a power plant with a thorium reactor is no cheaper than building a power plant with a uranium reactor. Further, using thorium in existing reactors is technically possible, but it would not provide any clear commercial benefit and would require other new infrastructure.
Additionally, there is technically no such thing as a thorium reactor. Thorium has no isotopes that readily fission to produce energy. So thorium is not usable as a fuel directly, but is instead a fertile nucleus that can be converted to uranium in a reactor. Only after conversion to uranium does thorium become useful as a nuclear fuel. So, even for a reactor that would use thorium within its fuel cycle, most energy produced would actually come from uranium fissions.
Claim: Next generation thorium reactors would be safer than current reactors.
True but misleading. Nuclear energy is already very safe, and Yang is correct about that. The current US nuclear fleet generates about 20 percent of all electricity in the United States and has an excellent safety record—despite accidents such as Three Mile Island. When it comes to new reactors, although some next-generation designs offer potential safety benefits relative to current reactors, they could be operated in either thorium-uranium or uranium-plutonium fuel cycles. Consequently, the benefits are a function of the inherent safety in the next-generation designs, not the utilization of thorium.
Claim: The waste from thorium reactors would be easier to deal with than waste from today’s uranium reactors.
False. A comprehensive study from the US Energy Department in 2014 found that waste from thorium-uranium fuel cycles has similar radioactivity at 100 years to uranium-plutonium fuel cycles, and actually has higher waste radioactivity at 100,000 years.
Claim: Thorium would be more proliferation-resistant than current reactors—you can’t make nuclear weapons out of it.
False. A 2012 study funded by the National Nuclear Security Administration found that the byproducts of a thorium fuel cycle, in particular uranium 233, can potentially be attractive material for making nuclear weapons. A 2012 study published in Nature from the University of Cambridge also concluded that thorium fuel cycles pose significant proliferation risks.
Claim: Building new nuclear reactors will likely be necessary if the United States wants to achieve net-zero emissions by 2049.
True. Nuclear energy is already the primary ultra-low carbon energy source for base-load electricity generation. Although solar and wind have their place in the energy mix, the primary benefit of nuclear energy is that it is not intermittent, as solar and wind are, so it is almost always available without needing energy storage. So new nuclear reactors will be necessary to both replace aging ones and to meet a net-zero carbon emissions goal. But thorium-uranium fuel cycles provide no inherent benefits relative to uranium-plutonium fuel cycles, so the new reactors need not be thorium-powered.