The separation of Pu from U in spent fuel processing by the reductive stripping of Pu(IV) from a TBP solvent phase is a very well established technology. Typical reducing agents include ferrous sulphamate, uranous nitrate/hydrazine, and hydroxylamine. Much fundamental data are available, and plants using these processes have been successfully operated for many years. Current Purex reprocessing plants use several solvent extraction cycles to purify the U and Pu products. Requirements for the development of future Purex processes for LWR and fast reactor fuel processing, or waste conditioning (e.g., the UREX process) include the use of single-cycle flowsheets intensified (centrifugal) contractors and the flexibility to meet different scenarios (e.g., coprocessing or low DFs on the Pu stream). In such "advanced" flowsheets, one option is to replace the reductive stripping of Pu by complexation-Pu(IV) is selectively complexed by a hydrophilic ligand and stripped in to the aqueous phase. The advantages of complexation include fast kinetics, temperature insensitivity compared to redox reactions and no reoxidation of Pu(III); therefore, there is no need for a stabilizer and likely improved criticality control. Indeed work on Pu and Np stripping using complexants, namely, hydroxamic acids, has been undertaken by BNFL for over a decade.
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