 A gas centrifuge is a separating machine specifically developed to separate Uranium-235 from Uranium-238. The gas centrifuge relies on the principles of centripetal force accelerating molecules based upon mass. When performed in a column, this yields separations of each component. The gas centrifuge was developed to replace the gaseous diffusion method of Uranium-235 extraction. The significant advantage of the gas centrifuge is that it relies on multiple centrifugal runs using cascades of centrifuges. This process yields higher concentrations of the Uranium-235 isotopes with significantly less energy usage compared to the previous gaseous diffusion process.
Centrifugal process (How it works)
The centrifugal process relies on the effect of simulating gravity (using centripetal acceleration) to separate molecules according to their mass, and can be applied to both liquid and gaseous materials. Forces are applied by placing material inside a mechanism that rotates the material at high speed.
Gas centrifugation process
The gas centrifugation process utilizes a unique design that allows gas to constantly flow in and out of the centrifuge. Unlike most centrifuges which rely on batch processing, the gas centrifuge utilizes continuous processing, allowing cascading, in which multiple identical processes occur in succession. The gas centrifuge consists of a cylindrical rotor, a casing, an electric motor, and three lines for material to travel. The gas centrifuge is designed with a casing that completely encloses the centrifuge. The cylindrical rotor is located inside the casing, which is evacuated of all air to produce a near frictionless rotation when operating. The motor spins the rotor, creating the centripetal force on the components as they enter the cylindrical rotor. There are two output lines, one located at the top of the centrifuge and the other located at the bottom. The heavier molecules will segregate to the bottom of the centrifuge while the lighter molecules will segregate to the top of the centrifuge. The output lines take these separations to other centrifuges to continue to the centrifugation process.
 Cascade of gas centrifuges used to produce enriched uranium. U.S. gas centrifuge plant in Piketon, Ohio, 1984.
Separative work units (SWU)
The Separative Work Unit (SWU) is a measure of the amount of work done by the centrifuge and has units of mass (typically kilogram separative work unit). The work WSWU necessary to separate a mass F of feed of assay xf into a mass P of product assay xp, and tails of mass T and assay xt is expressed in terms of the number of separative work units needed, given by the expression
- where
 is the value function, defined as
Practical application of centrifugation: Separating Uranium-235 from Uranium-238
The separation of uranium requires a gaseous form, Uranium hexafluoride (UF6). Upon entering the centrifuge, the lighter Uranium-235 isotope collects towards one end of the centrifuge while the heavier Uranium-238 isotope at the other. The enriched uranium is upstream to another centrifuging stage and the depleted uranium downstream to the previous stage. Usually, enrichments plants may include thousands of centrifuges arranged in cascades.
History of the gas centrifuge
Suggested in 1919, the centrifugal process was first successfully performed in 1934. J.W. Beams and co-workers at the University of Virginia developed the process by separating two chlorine isotopes through a vacuum ultracentrifuge. Although the Manhattan Project abandoned this theory during the development of the first nuclear weapons, the gas centrifuge uses much less energy than previous methods of separation. The Nuclear program in the Soviet Union uses this advanced technology as the primary way to obtain enriched uranium since 1945. |
