Helikon vortex separation process

Process

In the Helikon vortex separation process, a gas mixture of uranium hexafluoride and hydrogen is fed at near-sonic speeds through nozzles or holes into one end of a tube, entering at a tangent. The tube narrows to a small opening at one or both ends. This tangential feed creates a spiraling vortex inside the tube, and two gas streams are drawn off from opposite ends. Isotopic separation is achieved by centrifugal force. Friction against the tube wall causes the swirling flow to slow down downstream from the feed point, so the tube’s inner diameter is usually tapered to help maintain the vortex speed. The process uses a very small stage cut—the ratio of product flow to feed flow is about 1/20—and operates at high pressures. Because linking individual stages requires extremely complex plumbing, the design was adapted into a cascade called Helikon, where 20 separation stages are grouped into a single module that shares two axial-flow compressors. For this to work, the compressors must move parallel gas streams with different isotopic compositions without letting them mix significantly. A typical Helikon module is a large steel cylinder containing the 20 separator assemblies, one compressor at each end, and two water-cooled heat exchangers. The process has no criticality concerns because the feedstock is highly diluted, and it works well for batch processing. As a result, Helikon plants can be built relatively small, which raises nuclear proliferation concerns.