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The inner-sphere mechanisms of the disproportionation reactions of U(V), Np(V), and Pu(V) ions have been studied using a quantum mechanical approach. The U(V) disproportionation proceeds via the formation of a dimer (a cation-cation complex) followed by two successive protonations at the axial oxygens of the donor uranyl ion. Bond lengths and spin multiplicities indicate that electron transfer occurs after the first protonation. A solvent water molecule then breaks the complex into solvated U(OH)2(2+) and UO2(2+) ions. Pu(V) behaves similarly, but Np(V) appears not to follow this path. The observations from quantum modeling are consistent with existing experimental data on actinyl(V) disproportionation reactions.

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Over the last decade there has been much interest in the applications of diglycolamide (DGA) ligands for the extraction of the trivalent lanthanide and actinide ions from PUREX high active raffinates or dissolved spent nuclear fuel. Of the DGAs, the N,N,N',N'-tetraoctyldiglycolamide (TODGA) is the best known and most widely studied. A number of new actinide separation processes have been proposed based on extraction with TODGA. This review covers TODGA based processes and extraction data, specifically focusing on how phase modifiers have been used to increase metal loading and thus enhance the operating process envelopes. Effects of third phase formation and the organic phase speciation are reviewed in this context. Relevant aspects of the extraction chemistry of important solvents (TODGA-modifier-diluent combinations) are described and their performances demonstrated by a consideration of the published flowsheet tests. It is seen that modifiers are successfully enabling the use of TODGA in actinide separation processes but to date the identification and testing of suitable modifiers has been rather empirical. There is a growing understanding of the fundamental chemistry occurring in the organic phase and how that affects extractant speciation and metal loading capacity but studies are still needed if TODGAbased flowsheets are to become an industrially deployable option for minor actinide (MA) recovery processes.

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