Overview

Thorium was discovered in 1828 by the Swedish chemist Jons Jacob Berzelius, in a black mineral sent to him from Norway by the mineralogist Morten Thrane Esmark. Berzelius named it after Thor, the Norse god of thunder. Its radioactivity was demonstrated in 1898, by Gerhard Carl Schmidt and, independently, Marie Curie. Thorium is a dense, silvery, weakly radioactive metal, once widely used in incandescent gas mantles and long studied as a potential fuel for nuclear reactors. Several times more abundant than uranium in the crust, thorium once brightened the mantles of gas lamps and stiffened optical glass, and its capacity to breed nuclear fuel keeps it under study as the basis of a potentially safer and more plentiful reactor cycle.

India has pursued thorium reactor research more seriously than most nations, since its coastal monazite sands hold some of the world's largest thorium reserves relative to its comparatively modest uranium deposits, and its long-term nuclear programme has explicitly planned around an eventual thorium fuel cycle since the 1950s. Earlier, the United States ran a molten-salt reactor at Oak Ridge National Laboratory through the 1960s specifically to test thorium as a fuel, a promising demonstration ultimately abandoned when Cold War strategic priorities favoured uranium and plutonium reactor designs capable of also producing weapons material.