Countdown to Zero Day: Stuxnet and the Launch of the World's First Digital Weapon

by Kim Zetter

Centrifuges are metal cylinders with rotors inside that can spin at speeds in excess of 100,000 revolutions per minute to enrich uranium hexafluoride gas, produced from uranium ore found in earth and seawater. The hexafluoride gas is piped into “cascades” of centrifuges—groups of centrifuges connected by pipes and valves. And as the rotors inside them spin, the centrifugal force separates the slightly lighter U-235 isotopes in the gas—the fissile isotopes needed for atomic energy—from the heavier U-238 isotopes, in a process likened to panning for gold.23 Gas containing the heavier isotopes gets pushed to the outer wall, while gas containing lighter isotopes gathers closer to the center. Coils wrapped around the outside of the centrifuge that are filled with heated water create a varying temperature that sets the gas in vertical motion, in an oval pattern along the wall of the centrifuge, to further separate the isotopes. Scoops divert the gas containing the concentration of lighter isotopes into other centrifuges at a “higher” stage in the cascade, where further separation occurs, while the heavier gas, the depleted uranium, is diverted into a second set of centrifuges in a lower stage of the cascade for further separation. When additional U-235 isotopes are separated from this gas, it gets fed back into the higher stages to be recombined with the other U-235 isotopes while the depleted gas is sent to “waste”—that is, the tail end of the cascade, where it gets discarded. ...