Demonstration of Uranium(VI)/Plutonium(IV) Separation via Solvent Extraction by D2EHiBA in Annular Centrifugal Contactors

The use of N,N-dialkylamides as alternatives for tri-n-butyl phosphate (TBP) as extractants in the reprocessing of spent nuclear fuel has been investigated since the 1960s. N,N-di-2-ethylhexyl isobutyramide (D2EHiBA) and N,N-di-2-ethylhexyl n-butyramide (D2EHBA) can selectively extract hexavalent and tetravalent actinides from nitric acid spent nuclear fuel solutions. Annular centrifugal contactors (ACCS) have been designed specifically for counter-current multi-stage solvent extraction in the nuclear sector. Their main advantages are a high stage efficiency, the ability to work at short residence times (seconds), and a small liquid hold-up. In the present study, a new D2EHiBA-based separation of hexavalent uranium from tetravalent plutonium was investigated using ACCs, where for safety and practical reasons the use of hydrazine or other reductant/complexant is avoided altogether. The extraction behavior of technetium-99 m, ruthenium-103, and americium-241 was also monitored under those process conditions. It was demonstrated that uranium(VI) can be quantitatively extracted and purified from plutonium(IV) using the D2EHiBA extractant. A U(VI)/Pu(IV) decontamination factor of more than 6000 was obtained. The excellent performance of the modified lab-scale BXP012 annular centrifugal contactors was demonstrated, and these contactors have proven to be a valuable tool in the upscaling of solvent extraction processes at the Belgian Nuclear Research Center (SCK CEN).