what is uranium enrichment? what is the use of centrifuge in it?

Answer 1

Uranium exists in two naturally occuring isotopes. U235 and U238. U235 (a minor component, 0.7%) is useful for making nuclear weapons and for use in nuclear power-plants. U238 is not directly usable in either application (although it can be converted into plutonium), so you have to get rid of the U238. Since the U235 is such a low percentage you have to "enrich" it--typically to 10-20% for commercial power plants and 95+% for bombs.

You convert the uranium to uranium hexafluoride (because it's non-reactive, even though it's ridiculously toxic), and then by spinning the UF6 in centrifuges, in which the centrifugal force pushes on the heavier U238 more than on the U235, you enrich, a tiny little bit at a time, the U235 from the U238. You do this repeatedly until you get sufficient enrichment, then chemically convert the uranium hexafluoride back into plain uranium.