Solubility classification of airborne products from uranium ores and tailings piles

Airborne products generated at uranium mills were assigned solubility classifications for use in the ICRP Task Group Lung Model. No significant difference was seen between the dissolution behavior of airborne samples and sieved ground samples of the same product. If the product contained radionuclides that dissolved at different rates, composite classifications were assigned to show the solubility class of each component. If the dissolution data indicated that a radionuclide was present in two chemical forms that dissolved at different rates, a mixed classification was assigned to show the percentage of radionuclide in each solubility class. Uranium-ore dust was assigned the composite classification: (235U, 238U) W; (226Ra) 10% D, 90% Y; (230Th, 210Pb, 210Po) Y. Tailings-pile dust was classified: (226Ra) 10% D, 90% Y; (230Th, 210Pb, 210Po) Y. Uranium octoxide was classified Y, uranium tetrafluoride was also classified Y, ammonium diuranate was classified D, and yellow-cake dust was classified (235U, 238U) 60% D, 40% W. The term yellow cake, however, covers a variety of materials which differ significantly in dissolution rate. Solubility classifications based on the dissolution half-times of particular yellow-cake products should, thus, be used when available. The D, W, and Y classifications refer to biological half-times for clearance from the human respiratory tract of 0 to 10 days, 11 to 100 days, and > 100 days, respectively