Helikon vortex separation process

The Helikon vortex separation process is an aerodynamic uranium enrichment process designed around a device called a vortex tube. This method was designed and used in South Africa for producing reactor fuel with a uranium-235 content of around 3–5% in addition to making 80–93% enrichment for the weapons program. The Uranium Enrichment Corporation of South Africa, Ltd. (UCOR) which developed the process operated a facility at Valindaba (known as the 'Y'plant) to produce hundreds of kilograms of HEU. Aerodynamic enrichment processes require large amounts of electricity and are not generally considered economically competitive as it has high specific-energy consumption and substantial requirements for removal of waste heat. The South African enrichment plant has apparently been closed.

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Process

In the vortex separation process a mixture of uranium hexafluoride gas and hydrogen is injected tangentially into a tube, at one end through nozzles or holes at velocities close to the speed of sound. The tube tapers to a small exit aperture at one or both ends. This tangential injection of gas results in a spiral or vortex motion within the tube, and two gas streams are withdrawn at opposite ends of the vortex tube; centrifugal force providing the isotope separation. The spiral swirling flow decays downstream of the feed inlet due to friction at the tube wall. Consequently, the inside diameter of the tube is typically tapered to reduce the decay in the swirling flow velocity. This process is characterized by a separating element with very small stage cut (ratio of product flow to feed flow) of about 1/20 and high process-operating pressures.

Due to the extremely difficult plumbing required to link stages together, the design was developed into a cascade design technique, called Helikon in which 20 separation stages are combined into one module, and all 20 stages share a common pair of axial-flow compressors A basic requirement for the success of this method is that the axial-flow compressors successfully transmit parallel streams of different isotopic compositions without significant mixing. A typical Helikon module consists of a large cylindrical steel vessel housing the 20 separator assemblies, along with two compressors (one mounted on each end), and two water-cooled heat exchangers.

The advantages of this process are the lack of criticality concerns due to the highly diluted feedstock and its suitability for batch processing. This latter ability means plants can be relatively small, making this technology a nuclear proliferation concern.

See also

• South Africa and weapons of mass destruction
• Nuclear reprocessing
• Nuclear fuel cycle
• Nuclear power