Yellowcake is a solid uranium-oxygen compound (U3O8) that takes its name from its color and texture. It is a product of the uranium milling process, essentially a half-way step between raw ore finished product. It is the material used for fuel enrichment and fuel pellet fabrication for nuclear reactors.

The raw ore is crushed and then washed with sulfuric acid, mixed with ammonia gas and then precipitated. The floury precipitate thus collected is yellowcake.

To obtain the valuable uranium-235 from yellowcake, one must separate it from the non-fissionable isotopes uranium-238 (over 99% of all natural uranium) and uranium-234 (less than 0.01%).

Material from several sources including
http://www.nrc.gov/NRC/EDUCATE/GLOSSARY/Yellowcake.html
and
http://chemistry.about.com/science/chemistry/library/weekly/aa061200a.htm.

Introduction

Following the refinement process described by Lord Brawl in the writeup above, "yellowcake" uranium must be further converted and purified into other chemical compounds before it is a particularly useful material. The fact that it can be further refined, and that these refinement processes are well-known is one reason why yellowcake has become a major "credibility gap" question mark in recent world events, following the second Gulf War.

The Science

The two methods used to convert yellowcake both involve reacting the material with the gas fluorine. Generally, it is turned either into the gaseous uranium tetrafluoride (UF4) or uranium hexafluoride (UF6).

If converted into uranium hexafluoride, it then becomes the basic compound used in isotope separation for nuclear plants. However, if converted into uranium tetrafluoride, the resulting compound is generally used to make uranium metal -- and therein exists the danger, as this reaction could be reproduced to create fissionable material for a nuclear bomb.

The chemical process used to create uranium tetrafluoride is written out as:

UO2(s) + 4HF(g) --> UF4(s) + 2H2O(g)


At this point, to create uranium metal from UF4, the compound must go through a reduction process. The newly-created uranium metal, if resulting in enough material, could end up being enough to achieve critical mass in a nuclear warhead.

The Relevance

Yellowcake has been in the news in recent months, following the apparent gaffe by the U.S. Government in the search for "weapons of mass destruction" following the Iraqi war. It was known that, in the 1980s, Iraq purchased 300 tonnes of yellowcake from Niger, but following Desert Storm, this uranium was accounted for, and Iraq's nuclear weapons program was dismantled. The "evidence" now being questioned in Washington and around the world, however, is about intelligence reports that Iraq was once again trying to procure yellowcake from Niger in 2001. As it turns out the intelligence reports were never substantiated -- and in fact, some in the upper ranks of Washington, including those in the State Department -- found no credibility in these reports.

Nonetheless, said intelligence made its way into George W. Bush's public statements. In turn, this, the notion that Iraq was attempting to procure nuclear materials, in turn became a "selling point" to the American public and the world for military action in Iraq.




Works Referenced:
  • "A Question of Trust" (Time Magazine) : http://www.time.com/time/covers/1101030721/story2.html
  • Identification and Description of Mineral Processing Sectors and Waste Streams" (United States Environmental Protection Agency) : http://www.epa.gov/epaoswer/other/mining/minedock/id/id4-ura.pdf

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