Peter Reinhardt writes about the energy prospects of thorium, a naturally occurring radioactive element that's much more abundant on Earth than uranium.
The important point is that thorium is ridiculously more abundant than uranium. And abundance matters when we're talking about providing energy to the world. In fact, there's so much thorium on Earth that the easily extractable reserves in the United States (10% of the world's) could supposedly power the entire United States at current energy levels for the next 10,000 years. It's not exactly renewable, but it's a much longer lifeline than oil. And it can be mined safely within US borders: most of the US reserves are concentrated in a 25 square-kilometer pileup of mountains straddling the border of Idaho and Montana.