Yellowcake

Production process

Traditional uranium mining involves extracting raw uranium ore through conventional methods, which remains common practice at many sites. The production process begins with crushing the ore to a fine powder using crushers and grinders to create "pulped" ore. This material then undergoes treatment with concentrated acid, alkaline, or peroxide solutions to leach out the uranium. In modern operations, approximately half of yellowcake production utilizes in situ leaching, where solutions are pumped directly through uranium deposits without physical excavation.

Composition

Early yellowcake compositions were not well characterized. As late as 1970, the U.S. Bureau of Mines defined yellowcake simply as the final precipitate from the milling process, presumed to be ammonium diuranate or sodium diuranate. The actual composition varies significantly based on leaching agents and precipitation conditions. Identified compounds in yellowcake include uranyl hydroxide, uranyl sulfate, sodium para-uranate, and uranyl peroxide, along with various uranium oxides. Contemporary yellowcake typically consists of 70% to 90% triuranium octoxide (U3O8) by weight, with other oxides such as uranium dioxide (UO2) and uranium trioxide (UO3) also present.

Yellowcake production occurs in all countries where uranium ore is mined.

Further processing

Yellowcake serves as feedstock for nuclear fuel production. For use in reactors, it is smelted into purified UO2 for fabrication into fuel rods, particularly for pressurized heavy-water reactors and other systems utilizing natural unenriched uranium.

For enrichment purposes, uranium oxides are converted to uranium hexafluoride gas (UF6) through fluorination. This gas then undergoes isotope separation via gaseous diffusion or gas centrifuge processes. These methods can produce low-enriched uranium (up to 20% U-235) suitable for most commercial power reactors. Additional processing yields highly enriched uranium (20% or more U-235) for naval propulsion systems. Further refinement can produce weapons-grade uranium (typically 90% U-235) for nuclear weapons.

Radioactivity and safety

Yellowcake consists primarily (99%) of U-238, which has relatively low radioactivity. With a half-life of 4.468 billion years, U-238 emits radiation slowly. At this processing stage, before U-235 concentration, the material's radioactivity matches its natural state when underground, maintaining native isotopic ratios. While generally stable, yellowcake poses inhalation hazards.

References

References

1. "Yellowcake". U.S. Nuclear Regulatory Commission.
2. "Yellowcake". European Nuclear Society nuclear glossary.
3. Hausen, Donald M.. (1998). "Characterizing and Classifying Uranium Yellow Cakes: A Background". [[JOM (journal).
4. Gil, Laura (2018), [https://www.iaea.org/sites/default/files/publications/magazines/bulletin/bull59-2/5922223.pdf "Uranium leaching: How yellowcake is made"] {{Webarchive. link. (2022-11-29 , IAEA Bulletin (Online), vol. 59, iss. 2, pp. 22-23.)
5. (February 2013). "Health Effects". Agency for Toxic Substances and Disease Registry (US).