Traveling wave reactor

Burns U-238 instead of U-235. [Link]

When we dig uranium out of the ground, 99% of it is U-238, which we don't care about. 1% of it is U-235, which we use for all kinds of things, including conventional reactor fuel. Bill Gates and some of his pals figure that it would be a much better idea if we could just burn the U-238 instead.
Using U-238 as fuel wasn't Bill's idea, but it's taken until recently for supercomputers to figure out how to make the reaction work properly. Based on these new data, Gates helped fund a startup called Terrapower, which is attempting to build the first prototype of a new type of nuclear reactor called a "traveling wave" reactor.
A traveling wave reactor gets its name from how the nuclear reaction propagates through the reactor's fuel. A bunch of rods of U-238 are placed in a big cluster, and a rod of U-235 (just one) kick starts the whole thing. The U-238 gets converted to plutonium 239, which generates heat keeps the reaction going, and as the reaction propagates outwards in a sort of wave, more rods of U-238 get shuffled into the middle. And after the fuel gets all used up, you can take it out and use it to kick start a new reactor.