Uranium enrichment and reprocessing - oh yea!

Fasten your seatbelts. Below is more than you ever wanted to know about the process of uranium enrichment and reprocessing. Though the U.S. doesn't currently reprocess spent nuclear fuel, there is a movement to begin doing so. It's coinciding with the growing potential of nuclear as a renewable energy source, and the Department of Energy is all for it. It's also pinned to the Yukka Mt. dilemma, which is the long-term geologic repository for radioactive waste from nuclear reactors that's still....not.....open. Over 100 reactors in the U.S. are storing their nuclear waste on-site, waiting for Yukka to open its underground doors to unwanted nuclear fission materials. Except that the nuclear waste is full of more fissionable energy and can be recycled (reprocessed) to convert into electricity. France, Russia and Germany reprocess spent nuclear waste into new fuel. 

Nuclear enrichment is increasing the concentration of the fissile U-235 in uranium supply. Uranium ore is .72% U-235 and roughly 99% U-238 (does not fission). Fuel rods for nuclear reactors is made from uranium enriched to about 4% U-235.  There are two significant processes - gaseous diffusion and gas centrifuge.

Diffusion was developed during the Manhattan Project in the 1940s. It converts uranium into UF6 -uranium hexafluoride - gas. Gaseous UF6 is fed into 100s of porous membrane barriers and the lighter U-235 molecules penetrate microscopic holes in the barriers, whereas heavier U-238 molecules are left behind. This creates a more concentrated stream of U-235, which is further enriched in the next stage, and a depleted stream of mainly U-238, which is re-harvested for more U-235.

Gas centrifuge uses many tall rotating cylinders that are interconnected in cascade formations. Simple, eh? Gaseous UF6 is fed down into the rotor, which is surrounded by evacuated casing, and spinned at a tremendously fast speed. Faster than your mind is even processing this. The centrifugal force causes the gas to move towards the wall of the rotor. The heavier U-238 molecules move closer to the wall, leaving lighter U-235 molecules in the center. The U-235 stream is withdrawn and fed into a higher stage. Centrifuge enrichment requires many cascade stages, but has a short equilibrium time and enriches faster. The plants are less cumbersome to develop but also to detect. Iran is using centrifuge technology and we have no idea how far along the enrichment process they are, do we? 

The political and moral question is this: how do you encourage the development of nuclear energy, which requires uranium enriched to 4%, and prevent the construction of nuclear warheads, which use uranium enriched to 90%? 

There's no time to discuss reprocessing today, but we'll get to that. Before the U.S. does. Maybe.