Diffusion techniques
Gaseous Diffusion:
The Uranium is made into a gaseous form by being converted into UF6. These contain U-235 atoms which are slightly lighter and will diffuse through each barrier at a higher rate than those containing U-238 atoms. The difference in mass and velocity between the UF6 molecules containing either U-235 or U-238 is very small and so thousands of stages are needed in order to build on the enrichment achieved by the ones before it and also to more efficiently make use of the depleted Uranium stream. Thermal Diffusion: This utilises the transfer of heat across a thin liquid or gas to accomplish isotope separation. The process exploits the fact that the lighter U-235 gas molecules will diffuse towards a hot surface and the heavier U-238 gas molecules will diffuse towards a cold surface. |
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Gas Centrifuge:
Uranium hexafluoride gas is fed into rapidly spinning cylinders. Inside the rotating centrifuge, the heavier molecules containing U-238 atoms move preferentially towards the outside of the cylinder, while the lighter molecules containing U-235 atoms remain closer to the central axis. The gas in this cylinder is then made to circulate bottom to top driving the depleted Uranium near the outer wall towards the top while the gas enriched in U-235 near the centre is driven to the bottom. These 2 streams (one enriched and one depleted) can then be extracted from the centrifuge and fed to adjoining stages to form a cascade. Zippe Centrifuge: This technique is just an improvement on the standard gas centrifuge. The big difference is the use of heat. The bottom of the rotating cylinder is heated, producing convection currents that move the U-235 up the cylinder, where it can be collected by scoops. |