Uranium enrichment technologies

The enrichment of uranium has taken place since World War II, initiated by the quest for the atomic bomb to win the war. To enrich uranium means to separate the two main isotopes that make up natural uranium (U-235 and U-238). The details of the possible enrichment processes are generally classified because highly enriched uranium may be used for weapons production, but the principles are well known. The gaseous diffusion method developed during the war constitutes the first generation of uranium enrichment techniques and has been used both for enrichment to weapons grade uranium and also for production of low-enriched uranium for nuclear power plants. This technique has high energy consumption and takes up a lot of space and is therefore being phased out in favour of gas centrifuges. Gas centrifuges take up less space and use only about one tenth of the energy of the gaseous diffusion method. Gas centrifuges are harder to build technically, but once they are built they can more easily be used to produce highly enriched uranium, as well as low-enriched uranium, for weapons or other purposes. The gas centrifuge technology is spread around the world and has even been for sale on the black market. Laser isotope separation methods are about to become the third generation of commercial scale uranium enrichment technologies. These methods are researched by many countries, and have been developed to a great extent. The energy consumption of these processes is about the same as for gas centrifuges, but the facilities require much less space than the centrifuge plants. These are high-precision technologies, and making the lasers and other necessary equipment has posed significant technical challenges. It appears difficult to expand from laboratory scale to large scale facilities, and most of the research has been terminated. The only still active laser process is the SILEX process which is about to go commercial in a few years. Another technique which has been used on a large scale is the aerodynamic technique used in South Africa. This technique was used both for production of low-enriched and highly enriched uranium, but it is not regarded as commercially competitive because of its high energy consumption. Also the mass spectrometer method was used in a relatively large scale in the United States during World War II, but this process is too slow and consumes too much energy to be commercially competitive as well. The mass spectrometer method is relatively easy to perform, and could therefore be used in a non-commercial setting as a slow but reliable option for enrichment. This could also be said about the thermal diffusion method which was used to produce feed for the mass spectrometer method in the United States during World War II. The thermal diffusion method could not be used for high-level enrichment. Plasma processes have not been applied on a large scale yet. The chemical enrichment processes developed in France and Japan have been utilised in pilot plants, but not yet in full-scale facilities.