Nuclear Power Dossier: Conversion and Enrichment

Milled uranium is commonly called ‘yellowcake’, which describes its characteristic appearance. It still has a long journey to take – both in terms of processes and physically – before it can be used in a reactor. At the milling plant the yellowcake is packed in drums and shipped to a conversion plant. This is a highly risky business, because while yellowcake is the key ingredient for creating nuclear fuel, it is also a key ingredient for making nuclear weapons. It is worth considerably more than its weight in gold on the black market.

Enrichment is a process similar to distilling. Yellowcake contains only about 0.7 per cent uranium-235, the vital ingredient for nuclear fi ssion. In order to bring the concentration of uranium-235 up to the required 3.5 per cent, the oxide is mixed with fluorine and heated to form uranium hexafluoride, a gas commonly known as ‘hex’. While in this gaseous state the lighter molecules of uranium-235 are separated from the heavier uranium-238 by forcing them through a membrane with tiny openings. As it cools the enriched uranium returns to a solid state and is ready for conversion into fuel rods.