Thorium, formed by radioactive decay of uranium, is a naturally occurring radioactive metal found in rock, water, and soil. Found in monazite and other minerals, it’s 3X more abundant than uranium. Despite its radioactivity, small amounts of thorium were used in lantern mantles for brightness, ceramic glazes and welding rods. Until the 1950s, thorium dioxide was used as a contrast agent (i.e. Thorotrast) in medical radiology. Between 1930 and 1950, after 2.5 million people were injected with Thoroplast worldwide, resulting lifelong exposures to thorium produced higher than normal incidences of liver tumors. Inhalation of thorium dust by townspeople near mining operations also correlated with higher lung, pancreatic and bone cancer rates than unexposed towns.
After WWII, uranium-based nuclear reactors, similar to designs producing fissionable material for nuclear bombs, were repurposed to generate electricity. Thereafter, Washington approved an experimental molten salt reactor (MSR) using fissile material (U-233) generated by neutron bombardment of thorium. Built at Oak Ridge, a thorium-based MSR operated critically from 1965 to 1969. By 1973, however, Washington decided to discontinue thorium reactor research in favor of uranium technology, a decision to which nuclear physicists like Edward Teller and Ralph W. Moir objected. Alvin Weinberg, who guided development of the Oak Ridge MSR, lost his job as director of the national lab because he championed safer thorium reactor development without weapons applications. So, in the competition between fast-breeder liquid nuclear reactors (with riskier uranium-plutonium cycles) versus molten salt breeder reactors (with less-hazardous thorium-232), profit and militarism bested safety and cost-effectiveness. NASA scientist and thorium expert Kirk Sorensen concludes America would have achieved energy independence decades ago had the thorium path been chosen.
As anthropogenic climate crises multiply, so does our need for clean energy. Meeting that demand, in addition to conservation, renewable energy options (solar, wind, hydro, geothermal, tidal; bio-fuels) have dramatically cheapened, become more efficient and created a plethora of jobs. Yet, despite Fukushima, Chernobyl and other disasters, some consider nukes viable options to curb carbon emissions before it’s too late. Eminent scientists [e.g. NASA’s James Hansen, who posited the 350ppm CO2 atmospheric safety limit (now 410ppm and climbing), MIT’s Kerry Emanuel (MIT), and Carnegie’s Ken Caldeira] propose adding newer, safer nuclear technologies to accompany “renewables” for energy. Facility costs, life expectancies, construction timetables, magnitudes of accidents and half-lives of radioactive waste are strong cases against building new reactors with current technology. Smaller, modular MSRs that automatically shut down during accidents are clearly preferable. Because it can’t be split to form nuclear chain reactions itself, but “breeds” fissile uranium-233, thorium-232 MSRs negate the threat of meltdowns. Thorium-fuelled reactors produce less waste, and unlike radiation levels of spent uranium fuel rods, which have 100,000-year half-lives, thorium attenuates rapidly.
The U.S., China, France and Russia are currently and justifiably exploring MSRs, including liquid fluoride thorium reactors (LFTRs), for improved electricity-making safety and efficiency compared to conventional nukes. But MSRs are no panacea. The UK’s National Nuclear Lab (2010) and David Suzuki (2014 in Science Matters) consider thorium claims “overstated.” True: a Canadian design is currently in vogue overseas. It uses thorium and recycled uranium as fuel, but still produces radioactive, highly corrosive materials, and fissile byproducts for warheads, conceivably contributing to weapons proliferation. LFTRs are theoretically safer and more efficient than conventional reactors because fluoride salts will contain a nuclear reaction. But fluorine gases, which potentially could be released, are extremely lethal. Furthermore, getting enough MSRs on-line to partially slake our energy glut would take 30-50 years. Given the urgency of global warming, we’ve already misspent such luxury. If, given declining cost and proven effectiveness, green energy was given the same government subsidies as nuclear we’d be answering the climate call-to-arms posthaste. Investing in renewable and smart-grid technologies is safer, faster, and cheaper, short-term and long.
Scott Deshefy is a biologist, ecologist and two-time Green Party congressional candidate.