leached from the target cladding and then dissolved in nitric acid. A nitrate (NO3–) solution containing uranium, molybdenum, and all other fission products (except volatile gases such as iodine, Xe-133, krypton-85, and nitrogen oxides) is formed.
Additional processing steps are required to recover pure molybdenum. Molybdenum can be separated from the nitrate solution by any of several separation processes. Typical separation processes include adsorption of the molybdenum on ion exchange resins and solvent extraction. Mo-99 recovery yields from these separation processes typically exceed 85 to 90 percent. The adsorbed or extracted molybdenum is washed with an appropriate solution to remove residual fission products and uranium. The wash solution becomes waste. The adsorbed molybdenum is then removed from the separation medium using an appropriate solution and recovered as a highly pure Mo-99 product.
Waste management is similar for both the alkaline and acid dissolution processes. In the alkaline process, the sodium aluminate and dissolved or suspended fission products that pass through the alumina column are combined with the other fission product wastes and precipitated oxide residues. This waste is stored temporarily either as-is or put into a solid form (e.g., in cement). The waste stream from the acid dissolution process includes the separated cladding and liquid waste from the Mo-99 separation or extraction processes. This liquid waste can be stored in tanks or mixed with cement to immobilize it. Most of these process wastes are stored at producers’ sites or are transported to offsite storage facilities. As noted in Chapter 3, one producer (Nuclear Technology Products Radioisotopes in South Africa) is disposing of these wastes.
Approximately 97 percent of the uranium originally present in the targets ends up in the process waste. Consequently, the accumulating waste from Mo-99 production contains substantial quantities of HEU. Worldwide, tens of kilograms of this HEU waste are accumulating annually from Mo-99 production. This HEU could be recovered for reuse, but currently no producer has active plans to do so, presumably because it is less costly to purchase fresh HEU. Additionally, no Mo-99 producers currently downblend their HEU waste (by mixing it with natural or depleted uranium) to convert it to LEU.
Both the alkaline and acid dissolution processes have been proven to be effective through many years of use with HEU targets by the major isotope