“Thorium-Fueled Automobile Engine Needs Refueling Once a Century,” reads the headline of an October 2013 story in an online trade publication. This fantastic promise is just one part of a modern boomlet in enthusiasm about the energy potential of thorium, a radioactive element that is far more abundant than uranium.
Thorium promoters consistently extol its supposed advantages over uranium. News outlets periodically foresee the possibility of "a cheaper, more efficient, and safer form of nuclear power that produces less nuclear waste than today's uranium-based technology."
Actually, though, the United States has tried to develop thorium as an energy source for some 50 years and is still struggling to deal with the legacy of those attempts. In addition to the billions of dollars it spent, mostly fruitlessly, to develop thorium fuels, the US government will have to spend billions more, at numerous federal nuclear sites, to deal with the wastes produced by those efforts. And America’s energy-from-thorium quest now faces an ignominious conclusion: The US Energy Department appears to have lost track of 96 kilograms of uranium 233, a fissile material made from thorium that can be fashioned into a bomb, and is battling the state of Nevada over the proposed dumping of nearly a ton of left-over fissile materials in a government landfill, in apparent violation of international standards.
Early thorium optimism. The energy potential of the element thorium was discovered in 1940 at the University of California at Berkeley, during the very early days of the US nuclear weapons program. Although thorium atoms do not split, researchers found that they will absorb neutrons when irradiated. After that a small fraction of the thorium then transmutes into a fissionable material—uranium 233—that does undergo fission and can therefore be used in a reactor or bomb.
By the early 1960’s, the US Atomic Energy Commission (AEC) had established a major thorium fuel research and development program, spurring utilities to build thorium-fueled reactors. Back then, the AEC was projecting that some 1,000 nuclear power reactors would dot the American landscape by the end of the 20th century, with a similar nuclear capacity abroad. As a result, the official reasoning held, world uranium supplies would be rapidly exhausted, and reactors that ran on the more-plentiful thorium would be needed.
With the strong endorsement of a congressionally created body, the Joint Committee on Atomic Energy, the United States began a major effort in the early 1960s to fund a two-track research and development effort for a new generation of reactors that would make any uranium shortage irrelevant by producing more fissile material fuel than they consumed.
The first track was development of plutonium-fueled “breeder” reactors, which held the promise of producing electricity and 30 percent more fuel than they consumed. This effort collapsed in the United States in the early 1980’s because of cost and proliferation concerns and technological problems. (The plutonium “fast” reactor program has been able to stay alive and still receives hefty sums as part of the Energy Department's nuclear research and development portfolio.)
The second track—now largely forgotten—was based on thorium-fueled reactors. This option was attractive because thorium is far more abundant than uranium and holds the potential for producing an even larger amount of uranium 233 in reactors designed specifically for that purpose. In pursuing this track, the government produced a large amount of uranium 233, mainly at weapons production reactors. Approximately two tons of uranium 233 was produced, at an estimated total cost of $5.5 to $11 billion (2012 dollars), including associated cleanup costs.
The federal government established research and development projects to demonstrate the viability of uranium 233 breeder reactors in Minnesota, Tennessee, and Pennsylvania. By 1977, however, the government abandoned pursuit of the thorium fuel cycle in favor of plutonium-fueled breeders, leading to dissent in the ranks of the AEC. Alvin Weinberg, the long-time director of the Oak Ridge National Laboratory, was, in large part, fired because of his support of thorium over plutonium fuel.
By the late 1980’s, after several failed attempts to use it commercially, the US nuclear power industry also walked away from thorium. The first commercial nuclear plant to use thorium was Indian Point Unit I, a pressurized water reactor near New York City that began operation in 1962. Attempts to recover uranium 233 from its irradiated thorium fuel were described, however, as a “financial disaster.” The last serious attempt to use thorium in a commercial reactor was at the Fort St. Vrain plant in Colorado, which closed in 1989 after 10 years and hundreds of equipment failures, leaks, and fuel failures. There were four failed commercial thorium ventures; prior agreement makes the US government responsible for their wastes.
Where is the missing uranium 233? As it turned out, of course, the Atomic Energy Commission’s prediction of future nuclear capacity was off by an order of magnitude—the US nuclear fleet topped out at about 100, rather than 1,000 reactors—and the predicted uranium shortage never occurred. America’s experience with thorium fuels faded from public memory until 1996. Then, an Energy Department safety investigation found a national repository for uranium 233 in a building constructed in 1943 at the Oak Ridge National Laboratory. The repository was in dreadful condition; investigators reported an environmental release from a large fraction of the 1,100 containers “could be expected to occur within the next five years in that some of the packages are approaching 30 years of age and have not been regularly inspected.” The Energy Department later concluded that the building had “deteriorated beyond cost-effective repair. Significant annual costs would be incurred to satisfy current DOE storage standards, and to provide continued protection against potential nuclear criticality accidents or theft of the material.” More
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