Distribution behavior of U(VI), Pu(IV), Am(III), and Zr(IV) with N,N-dihexyl octanamide under uranium-loading conditions

While the tri-n-butyl phosphate (TBP)-based PUREX process has been the work horse of the nuclear fuel reprocessing industry for the Last four and a hal f decades, a few drawbacks associated with the use of TBP have caused conce rn to the separation scientists and technologists. These shortcomings may p ose a serious challenge particularly during the reprocessing of (a) short c ooled thermal reactor fuels, (b) fast reactor fuels with the larger Pu cont ent and significantly higher burn up, and (c) while treating various waste streams for their disposal to the environment. The N,N-dialkyl aliphatic am ides have received particular attention as alternate potential extractants for the reprocessing of spent nuclear fuels in view of (a) the innocuous na ture of their degradation products, namely, carboxylic acids/amines and (b) the possibility to incinerate the used solvent leading to reduced volume o f secondary waste. The physical and chemical properties of these amides are influenced strongly by the nature of alkyl groups. The extractant N,N-dihe xyl octanamide (DHOA) was found to be a promising candidate among a large n umber of extractants studied. Laboratory batch studies as well as mixer set tler studies were performed under process conditions with DHOA and compared with those of TBP. DHOA was found to extract Pu(IV) more efficiently than TBP, both at trace-level concentration as well as under uranium loading con ditions. In addition, the extraction behavior of Am(III) and Zr(IV) was stu died at varying nitric acid concentrations (1 to 6 M). Extraction behavior of uranium at macroconcentrations (9.9 to 157.7 g/l) was carried out at dif ferent temperatures, and it was observed that D-U decreased with the increa se in U loading as well as with the increase of temperature (in the range 2 5 to 45 degreesC) and that the two-phase reaction was exothermic in nature. Mixer settler studies on U(VI) revealed that DHOA is similar to TBP during the extraction cycle but better than TBP during the stripping cycle.