From Yellowcake to Nuclear Reactor Fuel

Uranium mining methods produce a liquid with uranium dissolved in it. This is filtered and the uranium is then separated by ion exchange, precipitated from the solution, filtered, and dried to produce a bright yellow uranium oxide concentrate known as ‘yellowcake,’ which contains 0.7% U235.

The vast majority of all nuclear power reactors require ‘enriched’ uranium fuel, in which the proportion of the U235 isotope has been raised from the natural level of 0.7% to about 3.5% to 5%. The enrichment method needs uranium in gaseous form, so the yellowcake goes through a conversion process in which the uranium oxide is turned into uranium hexafluoride gas.

This gas then goes through an enrichment process that concentrates the U235 by the centrifuge process, with thousands of rapidly spinning vertical tubes. As the tubes spin, the heavier U238 is spun farther from the center of the tube by centrifugal force and is discarded. The lighter U235 stays closer to the center and flows to the next centrifuge. To reach a useful level of U235, the gas must go through thousands of centrifuges, each of which slightly increases the concentration until it reaches the required level. Much more about the process is shown on the World Nuclear Associate website.