ENRICHMENT

Current enrichment technologies are based on either gaseous diffusion or centrifuge methods. Other methods based on curved nozzle separation and laser enrichment have also been explored (Leclercq, 1986). The capital costs of enrichment plants are relatively high; around 6% of the total generation cost (Bertel and Wilmer, 2003).

Gaseous diffusion is a widely used method of enrichment in many countries. In this process, uranium hexafluoride is enriched by diffusion through porous barriers. The process is repeated through a large number of stages until the required enrichment is obtained. Capital costs are therefore high. The engineering issues relate to constructing corrosion resistant and efficient barriers to prevent blocking of the pores. For the process to work efficiently, feed streams need to be compressed and then the heat of compression removed to maintain the gases at the correct temperature and pressure. This is an energy­intensive process and therefore gaseous diffusion plants have high operating costs because of their large electricity requirements.

In centrifuge plants the uranium hexafluoride gas is spun in a vertical centrifuge and the U-235 concentrated near the axis. The high rotational speeds place limits on centrifuge capacity and therefore many (thousands) of the identical centrifuges are required. Centrifuge plants are, therefore, also capital intensive. However, operating costs are less than for gaseous diffusion. The gas must be successively centrifuged in stages but the number of stages is approximately 10 times less. Also the operating energy requirements are 10 times less than for gaseous diffusion plants.

At the present time, there is a surplus of enrichment capacity in operation in the world, despite the fact that few companies operate enrichment plants and the number of plants is very small (Bertel and Wilmer, 2003). However some plants have been in operation for 25 years and will need to be replaced. The next generation of enrichment plants is likely to be based on centrifuge technology.

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