Abstract
This chapter concerns the development of the universal extraction (UNEX) process and some new variations in its application. Choice of synergistic additives and diluents for chlorinated cobalt dicarbollide (CCD) are discussed. The results of many tests with actual and simulated high-level wastes (HLW) were observed and compared. The use of regenerable stripping solutions containing methylamine carbonate allows simplification of the handling and a volume reduction in the high-level strip product. The replacement of carbamoylphosphine oxides by diamides of dipicolinic acid as constituents of the UNEX extractant makes it possible to use less expensive extractants which can also treat wastes with elevated concentrations of rare-earth elements (REE). Possibilities for radionuclide group separation by the UNEX process were investigated using different stripping solutions. In this way, the following group separations are possible: An+REE+Sr and, separately, Cs; An+REE and, separately, Cs+Sr; finally, Cs, Sr, and An+REE separately. Recovery of radionuclides into individual fractions permits their transformation into more stable storage matrices.
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