Thorium is a chemical element with the symbol Th and atomic number 90. It is a naturally occurring, slightly radioactive metal. It is estimated to be about three to four times more abundant than uranium in the Earth's crust.
Thorium was successfully used as an alternative nuclear fuel to uranium in the molten-salt reactor experiment (MSR) from 1964 to 1969 to produce thermal energy, as well as in several light-water reactors using fuel composed of a mixture of 232Th and 233U, including the Shippingport Atomic Power Station (operation commenced 1957, decommissioned in 1982). Currently, officials in the Republic of India are advocating a thorium-based nuclear program, and a seed-and-blanket fuel utilizing thorium is undergoing irradiation testing at the Kurchatov Institute in Moscow. Advocates of the use of thorium as the fuel source for nuclear reactors state that they can be built to operate significantly cleaner than uranium based power plants as the waste products are much easier to handle.