Yellowcake (also called Urania or Uranium)

Why Is Yellowcake Uranium Called Yellowcake???

Yellowcake or urania is a uranium powder obtained from leach solutions during uranium ore processing. Modern yellow cake consists of 70-90% uranium oxides. The material is called yellowcake because a drum of the powder produced by early uranium mining operations resembled a yellow cake. However, modern yellowcake usually is brown or black.

Photo: A drum of yellowcake uranium, viewed from above. (US Department of Energy)

Yellowcake (also called Urania or Uranium)

Yellowcake (also called urania) is a kind of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores. Typically yellowcakes are obtained through the milling and chemical processing of uranium ore forming a coarse powder which has a pungent odour, is insoluble in water and contains about 80% uranium oxide, which melts at approximately 2878 °C. Although uranium is one of the densest metals on Earth, yellowcake is relatively light, with a density approximately that of elemental sulfur.

The ore is first crushed to a fine powder by passing raw uranium ore through crushers and grinders to produce "pulped" ore. This is further processed with concentrated acid, alkaline, or peroxide solutions to leach out the uranium. Yellowcake is what remains after drying and filtering. The yellowcake produced by most modern mills is actually brown or black, not yellow; the name comes from the color and texture of the concentrates produced by early mining operations.

Initially, the compounds formed in yellowcakes were not identified; in 1970, the U.S. Bureau of Mines still referred to yellowcakes as the final precipitate formed in the milling process and considered it to be ammonium diuranate or sodium diuranate. The compositions were variable and depended upon the leachant and subsequent precipitating conditions. Among the compounds identified in yellowcakes include: uranyl hydroxide, uranyl sulfate, sodium para-uranate, and uranyl peroxide, along with various uranium oxides. Modern yellowcake typically contains 70 to 90 percent triuranium octoxide (U₃O₈) by weight. Other oxides such as uranium dioxide (UO₂) and uranium trioxide (UO₃) exist.

Yellowcake is used in the preparation of uranium fuel for nuclear reactors, for which it is smelted into purified UO₂ for use in fuel rods for pressurized heavy-water reactors and other systems that use natural unenriched uranium.

Purified uranium metal (not the uranium oxide) can also be enriched in the isotope U-235. In this process, the uranium is combined with fluorine to form uranium hexafluoride gas (UF₆). Next, that undergoes isotope separation through the process of gaseous diffusion, or in a gas centrifuge. This produces either: A. Somewhat enriched uranium containing about four percent U-235 that is suitable for use in large civilian electric-power reactors, or B. Highly-enriched uranium containing 90% or more U-235 that is suitable for use in compact nuclear reactors - usually used to power naval warships and submarines, or in nuclear weapons. However, since the collapse of the Soviet Union, there is a worldwide surplus of highly-enriched uranium, and not much is made anymore. All the large uranium diffusion plants in the United States, the former Soviet Union, and the United Kingdom have been closed, and some of them are being demolished. See the Oak Ridge Gaseous Diffusion Plant or K-25.

Yellowcake is produced by all countries in which uranium ore is mined