|Cascade of uranium centrifuges|
Uranium gas is fed into cascades of thousands of centrifuges comprising a rotor of 1 to 2 m high and 15-20 cm of diameter. When the rotors rotate at very high speeds, the molecules of uranium-238 tend to move more near the outside wall of the cylinder than those of uranium-235 around the cylinder axis. For an efficient separation, centrifuges should turn 50 000-70 000 revolutions per minute, a speed of the cylinder wall outside of 400-500 m per second. The slightly enriched fraction of one centrifuge will feed the next centrifuge, while the depleted fraction returns from the previous one.