Thorium

Slightly radioactive, stable in the atmosphere, soft, very ductile, lustrous, silvery gray-white, heavy metal in the actinide series of elements that retains its luster for several months and can be cold-rolled, swaged (process used to reduce the diameter of a metal and produce a taper), and drawn. When exposed to the atmosphere, it is important to note that thorium’s physical properties largely vary with the degree of contamination with the oxide form. Thorium is found in small amounts in most of the Earth’s rocks and soils. Of particular interest today is that it is several times more abundant than all isotopes of uranium combined. Although soil commonly contains thorium at an average of around 12 parts per million (ppm) those dilute deposits have no commercial value. Thorium occurs in several minerals including thorite (ThSiO₄), thorianite (ThO₂ + UO₂ is the most common thorium mineral), and as thorium dioxide (ThO₂) in monazite (a rare-earth and thorium phosphate mineral) that can contain up to about 12 percent thorium dioxide, which is the primary ore of thorium.

Historical Background: In 1828, Hans Morten Thrane Esmark (1801-1882), a Norwegian priest and mineralogist, found a rock he was unable to identify. That sample eventually wound up in the lab of the Swedish chemist, Jöns Jakob Berzelius, who analyzed the mineral and named it after Thor, the Norse god of thunder. In 1898, German chemist Gerhard Carl Schmidt and Polish-French physicist Marie Curie independently discovered thorium was radioactive. Between 1900 and 1903, Ernest Rutherford and Frederick Soddy, working at McGill University in Montreal, demonstrated how thorium decayed at a fixed rate over time into a series of other elements. Their discovery led to the identification of half life and led to their disintegration theory of radioactivity, which proposed that over time atomic nuclei of an unstable atom split to form other elements. That research into radioactive decay, coupled with the work of their colleague, Kasimir Fajans, resulted in the Radioactive Displacement Law of Fajans and Soddy that described the products of alpha and beta decay.

Author’s Note: Thorium began kicking up a lot of interest in the first decade of the 21^st Century due to its potential for use as a nuclear fuel. Several primary characteristics make thorium an excellent candidate to replace uranium as the fuel of choice in nuclear power plants: relative abundance, no costly processing requirements, better resistance to nuclear weapons proliferation, and an extraordinary efficiency as a nuclear fuel that translates to much less radioactive waste to clean up when the fuel is spent.

Real World Examples: Conflicting estimates as to the abundance of thorium have been issued by the USGS and the International Atomic Energy Agency (IAEA). Despite the lack of agreement as to particulars, both sources agree that the U.S, Turkey, Venezuela, and Australia possess considerable reserves but that Brazil and India most likely have the largest world’s known/estimated thorium deposits. In January 2013, Jiang Mianheng, a politically connected Chinese industrialist, was reported to be funding a $350 million project at China's National Academy of Sciences to develop thorium power that would use molten-salt reactors, as opposed to the uranium-fueled water reactors found in the U.S. That thorium fuel reactor technology, originally developed at the Oak Ridge National Laboratory in the 1960s but ultimately rejected for American applications, largely for political reasons, also used a molten-salt coolant, would be much cleaner environmentally (little dangerous waste) and meltdown-safe since the coolant material never reaches meltdown temperatures.