Light Water Nuclear Reactors (original) (raw)

Uranium Enrichment

Natural uranium is only 0.7% U-235, the fissionable isotope. The other 99.3% is U-238 which is not fissionable. The uranium is usually enriched to 2.5-3.5% U-235 for use in U.S. light water reactors, while the heavy water Canadian reactors typically use natural uranium. Even with the necessity of enrichment, it still takes only about 3 kg of natural uranium to supply the energy needs of one American for a year.

Uranium enrichment has historically been accomplished by making the compound uranium hexaflouride and diffusing it through a long pathway of porous material (like kilometers!) and making use of the slightly higher diffusion rate of the lighter U-235 compound. There have been tests of centrifugal separators, but modern efforts are directed toward laser enrichment procedures.

The uranium fuel for fission reactors will not make a bomb; it takes enrichment to over 90% to obtain the fast chain reaction necessary for weapons applications. Enrichment to 15-30% is typical for breeder reactors.