From - http://en.wikipedia.org/wiki/Thorium

"Thorium (pronounced / THOHR-ee-um) is a chemical element with the symbol Th and atomic number 90.

Thorium 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. It has been considered a waste product in mining rare earths, so its abundance is high and cost low.

Thorium was successfully used as a breeding (fertile) source for nuclear fuel – uranium (233) in the molten-salt reactor experiment (MSR) from 1964 to 1969 (producing thermal energy for heat exchange to air or liquids), as well as in several light water reactors using solid fuel composed of a mixture of 232Th and 233U, including the Shippingport Atomic Power Station (operation commenced 1957, decommissioned in 1982), but a thorium-uranium mix was only used at end of life to demonstrate Th-to-U breeding. Currently, the Japanese Fuji project and officials in 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, such as Nobel laureate Carlo Rubbia, state that they can be built to operate significantly cleaner than uranium-based power plants as the waste products are much easier to handle. According to Rubbia, a ton of thorium produces the same energy as 200 tons of uranium, or 3.5 million tons of coal. Edward Teller, co-founder and director of Lawrence Livermore National Laboratory, promoted thorium energy until his death, and scientists in France, Japan, India, and Russia are now creating their own thorium-based power plants. One leading commentator is calling for the creation of a new Manhattan Project, stating that the use of thorium fuel for energy would "reinvent the global energy landscape . . . and an end to our dependence on fossil fuels within three to five years."

When used in molten-salt reactors, thorium bred to 233U removes weaponization dangers, because no uranium exists in solid form and the reactor runs continuously, with no shutdown for refuelling—all thorium and fissile uranium is consumed and any undesired gases and uranium/plutonium isotopes are flushed out as gases (e.g., as uranium hexafluoride) as the hot, liquid salt is pumped around the reactor/exchanger system. ..."