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Yellowcake

Dateline: 06/12/00

By Alan Bruzel

Yellowcake is a product refined from uranium ore. Yellowcake contains a much higher percentage of uranium than does the ore, but is not of sufficient purity for nuclear reactors or nuclear weapons. And, for the purposes of this discussion, yellowcake marks a convenient halfway point between raw ore and usable product in the uranium purification process.

As it turns out, uranium is a fairly common metal. On average, it is about as abundant as tin. This makes uranium about 500 times more common than gold, and about forty times more prevalent than silver. The major uranium-containing mineral used for refining purposes is pitchblende, which happens to be the same mineral from which Martin Klaproth, in 1789, first identified this element, naming it for the newly-discovered planet Uranus (discovered in 1781 by William Herschel).

The real purpose behind uranium mining is to procure a product with a usable amount of uranium-235, which is uranium's fissionable isotope. Unfortunately, the natural occurrence of uranium-235 in uranium ores is only 0.71%, and it is present along with the non-fissionable isotopes uranium-238 (at 99.28%) and uranium-234 (at 0.01%). Nevertheless, it is uranium-235 that provides the energy that runs nuclear reactors. In turn, these nuclear reactors generate electricity. No uranium-235, no electricity.

Therefore, if one want uranium-235, one must go to uranium ores – where uranium is present in concentrations anywhere from 0.03 percent up to 12 percent – to first prepare a refined uranium product. This refined product is then enriched in uranium-235 and ultimately shipped to nuclear reactors.

A usual means of refining uranium ore is to first crush it into fine particles, convert the uranium oxides to sulfates with sulfuric acid, then to add ammonia gas and collect the precipitated ammonium diuranate. This yellow precipitate, having the texture of flour, is called yellowcake and contains from 60 to 90 percent uranium (a considerable improvement from 0.03 percent to 12 percent). At this point, yellowcake is packaged in 200-liter containers (55-gallon drums) and is sent off for further treatment.

Yellowcake, as shipped, is not yet ready for use as a nuclear fuel. Like the ore from which it comes, its uranium-235 content (0.71 %) is far too low to sustain a nuclear chain reaction. Nuclear power plants require an enriched product with 3 to 5% uranium-235, and weapons grade uranium needs to be further enriched to a uranium-235 content of 90% or more.

Therefore, the uranium salts in yellowcake are converted back into uranium oxides, which are reacted with hydrogen fluoride and fluorine to form uranium hexafluoride that is then heated to a gas. Separation of uranium-235 hexafluoride from the other uranium hexafluoride isotopes by either gaseous diffusion or gas centrifugation permits enrichment of this fissionable isotope. The uranium-235 enriched uranium hexafluoride is then chemically converted to uranium oxide for use in nuclear reactors, or to uranium metal for use in nuclear weapons.

What the Web Has to Say about:
Yellowcake

Facts on Minerals: Uranium
Background of this metal, and Australian uranium mines and mining. From the Minerals Council of Australia.

Iraq and the Bomb: Were They Even Close?
Probably not, as David Albright and Mark Hibbs report in The Bulletin of the Atomic Scientists, but at the time of the 1991 Gulf War, Iraq was producing and storing hundreds of metric tons of yellowcake.

Nuclear Fuel Cycle
Uranium mining, refining, enrichment, and uses of the final product. From the Uranium Institute.

Nuclear Sunset: The Economic Costs of the Canadian Nuclear Industry
David H. Martin and David Argue point out the failure of the Canadian nuclear industry to become economically self-sustaining. From the Campaign for Nuclear Phaseout.

Solubility Testing of Actinides
Yellowcake samples from different mills show different solubility profiles. From R.L. Metzger, B.H. Jessop, and B.L. McDowell, Radiation Safety Engineering.

Some Chemistry of Uranium
Chemical reactions uranium undergoes during its refining operations. From the Uranium Information Center.

Uranium
Facts about the uranium marketplace. From AMM.com.

Uranium Extraction Process
Energy Resources of Australia follows uranium processing from ore to yellowcake.

Uranium Fact Sheet
Key points concerning uranium deposits and the production of purified material. From World Wide Minerals.

Uranium Industry Annual 1999
The US uranium market: employment, production, prices, inventories. From the Energy Information Administration, US Department of Energy.

Uranium: Its Uses and Hazards
Isotopes, radioactive decay, and refining processes. From the Institute for Energy and Environmental Research.

Wide Brown Land Rich in Yellowcake
Past and future uranium mines in Australia. From Stuart Watt, Australian Broadcasting Corporation.

Wyoming Uranium: Fuel of the Future!
Uranium mining sites, methods of extraction, and mine operators. From the Wyoming Mining Association.

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