When discussing negotiations with Iran on nuclear weapons, uranium enrichment centrifuges often are mentioned. What are they?
The element uranium as it comes from the ground has two forms (two isotopes): U-235 and U-238. U-235 is much more important for creating the fission for nuclear power reactors and nuclear weapons.
Natural uranium contains less than 1% U-235, being predominately U-238. The process of increasing the percentage of U-235 is called enrichment. Because U-238 is heavier than U-235, centrifuges can be used to separate the two.
Nuclear power plants require enrichment to 3%-5%. Nuclear weapons require enrichment to at least 90%, and specially designed centrifuges are needed.