Named for the Norse god of thunder, thorium is a lustrous silvery-white metal. It’s only slightly radioactive; you could carry a lump of it in your pocket without harm. On the periodic table of elements, it’s along with other radioactive substances known as actinides. Thorium is abundant -- the US has at least 175,000 tons of the stuff -- and doesn’t require costly processing. It is also extraordinarily efficient as a nuclear fuel. As it decays in a reactor core, its byproducts produce more neutrons per collision than conventional fuel. The more neutrons per collision, the more energy generated, the less total fuel consumed, and the less radioactive nastiness left behind. Even better, you could use thorium in an entirely new kind of reactor, one that would have zero risk of meltdown.
http://www.wired.com/magazine/2009/12/ff_new_nukes/
