PNNL

Abstract

The Actinide Lanthanide SEParation (ALSEP) process is designed to separate the trivalent minor actinides from the aqueous stream generated after PUREX. The minor actinides and trivalent lanthanide fission products are coextracted, followed by selective stripping of the minor actinides. The lanthanides are subsequently removed from the ALSEP solvent for recycle of the solvent. Little is known about the behavior of U, Np, and Pu in the ALSEP process as it is intended for them to have been removed prior to implementing the ALSEP process. However, understanding their behavior is important since low concentrations of the major actinides will be present in the ALSEP feed due to small amounts of carryover that are almost inevitable in an industrial setting. The behavior of U(VI), Np(IV), Np(V), Np(VI), Pu(IV), and Pu(VI) was investigated in the three main sections of the ALSEP process – actinide/lanthanide co-extraction, actinide stripping, and lanthanide stripping. The tetravalent actinides were strongly extracted but were removed from the solvent along with the lanthanides by contacting the loaded solvent with an aqueous solution of N,N,N',N'-tetraethyldiglycolamide. Neptunium(V) quickly disproportionated when extracted. The hexavalent actinides were also strongly extracted but remained in the solvent through all sections of the ALSEP process. Methodology for removing the hexavalent actinides will need to be addressed for recycle of the ALSEP solvent in an industrial setting.