Radiological Safety Training for Uranium Facilities
Module 102 The Nuclear Fuel Cycle
processing and a mixture of low-grade crushed rock and sand called "mill
Only about 3 percent of the actual material removed from the mine ends
up as yellowcake, which means that millions of tons of mill tailings are
leftover. Yellowcake contains 70-90% by weight of uranium oxides. The
leftover mill tailings are a concern because they still contain some of the
uranium ore. Additional hazards exist due to the chemicals added.
It is estimated that the uranium milling in the United States left
approximately 138 million tons of mill tailings covering about 3,000 acres
The yellowcake slurry is then purified by either ion exchange or solvent
Following purification, the yellowcake slurry is dried, forming a
concentrated yellowcake compound that contains 75 - 98 percent uranium.
The yellow color is caused by the addition of leaching chemicals and their
eventual removal during the drying step. The final color can range from
yellow to orange to black depending on the chemicals used and the drying
The final color is a good indicator of solubility, and thus of biological
effects if uranium in this form is taken into the body. Less soluble uranium
compounds tend both to remain in the body longer and to be darker in
color. More soluble uranium compounds are removed from the body more
quickly by normal body functions, and tend to be lighter in color.