ABSTRACT

Separations of long-lived actinides play a pivotal role at different stages of nuclear fuel cycle, namely, (a) recovery and purification of fissile=fertile nuclides from their respective ores, (b) fuel reprocessing using processes such as PUREX=THOREX, (c) minor actinide partitioning, and (d) lanthanide-actinide separations. Their analytical separation is also an important step in chemical quality control of nuclear fuel materials and the estimation of the actinide elements in various waste streams. PUREX process employing tri-n-butyl phosphate (TBP) as extractant has been successfully employed for the industrial scale production of Pu from the spent fuels emanating from a variety of thermal and fast reactors. There is, however, only a limited experience in the recovery of 233U from irradiated Th using the THOREX process. However, separation scientists in nuclear industry are gearing up for the new challenges of reprocessing spent fuels discharged from Pu-based fast reactor fuels as well as Th-based advanced heavy water reactor fuels. Existing processes may have to be further modified to meet the demands of larger Pu content, larger radiation damage to the solvent, larger inventory of fission products, and above all the complex situation of dealing with a Th-Pu-U based ternary system. There is also a growing interest in the areas of partitioning of actinides from high-level waste. In view of its excellent track record, TBP continues to be the prime choice of separation scientists and technologists. However, its poor extractability of trivalent actinides, large secondary waste volumes, and interference of the degradation products in overall Pu recovery and decontamination from fission products are a cause of concern. The actinides, in particular, have a fascinating chemistry in solution (e.g., disproportionation, variable oxidation state, polymerization, etc.), which presents a stimuli as well as a challenge to the separation chemists. Hence, there is a need to develop alternative extractants, which are efficient, versatile, and

out selective separation of actinides or fission products from reprocessing=waste steams. Figure 31.1 shows some of the extractants employed for the recovery=purification of actinides in the nuclear fuel cycle or for analytical applications. In view of the high cost of some of these emerging extractants, it is imperative to develop simultaneously novel separation techniques, which employ relatively small inventory of extractants. Liquid membrane (LM)-based separations hold a particular promise toward this end [1-3].