page_title: Gas centrifuge
section_title: Gas centrifugation process
hierarchical_section_title: Gas centrifuge / Gas centrifugation process
caption_attribution_description: English: Cascade of gas centrifuges used to produce enriched uranium. This photograph is of the U.S. gas centrifuge plant in Piketon, Ohio from 1984.
context_page_description: A gas centrifuge is a device that performs isotope separation of gases. A centrifuge relies on the principles of centripetal force accelerating molecules so that particles of different masses are physically separated in a gradient along the radius of a rotating container.
  A prominent use of gas centrifuges is for the separation of uranium-235 from uranium-238. The gas centrifuge was developed to replace the gaseous diffusion method of uranium-235 extraction. High degrees of separation of these isotopes relies on using many individual centrifuges arranged in cascade, that achieve successively higher concentrations. This process yields higher concentrations of uranium-235 while using significantly less energy compared to the gaseous diffusion process.
context_section_description: The gas centrifugation process uses 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 uses 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. This force acts to separate the molecules of the gas, with heavier molecules moving towards the wall of the rotor, and the lighter molecules towards the central axis. There are two output lines, one for the fraction enriched in the desired isotope (in uranium separation, this is U-235), and one depleted in it. The output lines take these separations to other centrifuges to continue the centrifugation process.  The process begins when the rotor is balanced in three stages. Most of the technical details on gas centrifuges are difficult to obtain because they are shrouded in "nuclear secrecy".
  The early centrifuges used in the UK used an alloy body wrapped in epoxy impregnated glass fibre.  Dynamic balancing of the assembly was accomplished by adding small traces of epoxy at the locations indicated by the balancing test unit.  The motor was usually a pancake type located at the bottom of the cylinder.  The early units were typically around 2 metres long (approx.), but subsequent developments gradually increased the length.  The present generation are over 4 metres in length.  The bearings are gas-based devices, as mechanical bearings would not survive at the normal operating speeds of these centrifuges.
  A section of centrifuges would be fed with variable-frequency AC from an electronic (bulk) inverter, which would slowly ramp them up to the required speed, generally in excess of 50,000 rpm.  One precaution was to quickly get past frequencies at which the cylinder was known to suffer resonance problems.  The inverter is a high frequency unit capable of operating at frequencies around 1 kilohertz.  The whole process is normally silent; if a noise is heard coming from a centrifuge, it is a warning of failure (which normally occurs very quickly).  The design of the cascade normally allows for the failure of at least one centrifuge unit without compromising the operation of the cascade.  The units are normally very reliable, with early models having operated continuously for over 30 years.
  Later models have steadily increased the rotation speed of the centrifuges, as it is the velocity of the centrifuge wall that has the most effect on the separation efficiency.
  A feature of the cascade system of centrifuges is that it is possible to increase plant throughput incrementally, by adding cascade "blocks" to the existing installation at suitable locations, rather than having to install a completely new line of centrifuges.
caption: Cascade of gas centrifuges used to produce enriched uranium. U.S. gas centrifuge testbed in Piketon, Ohio, 1984. Each centrifuge is some 40 feet (12 m) tall. (Conventional centrifuges in use today are much smaller, less than 5 metres (16 ft) high.)
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