(334af) Radiolytic Degradation of Organic Solvents in the Actinide Lanthanide Separation Process (ALSEP) for Nuclear Waste Treatment

Hydrometallurgy, liquid-liquid separation, purification, actinide science, radiochemistry

Nuclear reactors provide an attractive option for significant baseload power generation with zero carbon emissions. However, treatment of operation radioactive byproduct is an ongoing challenge. The separation of highly radiotoxic, long-lived radioactive elements from used nuclear fuel (UNF) followed by their conversion into shorter-lived nuclides is instrumental in strengthening interest and public opinion towards nuclear power. Under current industrial processes utilizing liquid-liquid separation, the highly radiotoxic long-lived minor actinide elements, americium and curium, are not efficiently removed from UNF. The selective removal of the minor actinides is difficult due to the co-extraction of lanthanides, which significantly interfere with the treatment process. The Actinide Lanthanide Separation Process (ALSEP), consisting of the extracting organic solvent containing 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) in n-dodecane, was developed for the selective partitioning of minor actinides from the lanthanides. Due to the inherent radioactive nature of UNF, liquid-liquid separation systems must be resistant to ionizing radiation. Therefore, to improve our understanding under process operating conditions, the ALSEP extracting solvent was equilibrated with metal loaded acidic aqueous phase and subjected to gamma and alpha irradiation. Degradation dose constants revealed greater ligand degradation due to gamma than alpha irradiation, and equilibration with nitric acid did not significantly impact degradation kinetics. However, the presence of nitric acid appears to alter the degradation pathway by favoring the formation of higher molecular weight recombination products. Results revealed the greater radiolytic susceptibility of T2EHDGA over HEH[EHP] could disrupt the minor actinide recovery with increasing radiation exposure.