Screening of TODGA/TBP/OK solvent mixtures for the grouped extraction of actinides

The solvent combination N,N,N'N'- tetraoctyl diglycolamide (TODGA)/tributyl phosphate (TBP)/odourless kerosene (OK) is examined as a potential solvent system for a Grouped Actinide Extraction (GANEX) process to separate all of the actinides from fission products when reprocessing spent nuclear fuel. A series of solvent extraction batch experiments were performed with a range of TODGA/TBP/OK solvent combinations to assess the sensitivity of distribution values for a number of key elements towards [TBP] (0 - 1.1M), [TODGA] (0.1-0.4M), [HNO3] (0.1-5M) and heavy metal loading ([U] 0-200g/l). There is little impact on D-Am or D-Eu across the solvent range and no influence from U loading. Excellent D-Np values (> 10) are observed, increasing with increasing [TODGA], with [TBP] having little influence. Such high D-Np values may obviate the need for preconditioning of dissolved fuel feeds to control Np routing. High D-Tc values are found even at 5M HNO3, therefore Tc is expected to remain in the solvent phase. Both Pu(III) and Pu(IV) are readily extracted with D-Pu(III) > D-Pu(IV). Uranium is extracted by both TBP and TODGA and TBP is shown to effectively compete with TODGA for uranium coordination sites. Third phase formation occurs at high [U] loading and [HNO3] but is suppressed by increasing [TBP].