N,N-Dihexyl hexanamide:: A promising extractant for nuclear fuel reprocessing

N,N-Dialkyl amides have drawn the attention of radiochemists engaged in the development of alternate extractants to tri-n-butyl phosphate (TBP) for the reprocessing of irradiated fuels, particularly with high radiation fields and high plutonium content. Dihexyl hexanamide (DHHA) has been found to be a promising extractant in this direction. Log K-ex values for the extraction of UO2(NO3)(2). 2DHHA and Pu(NO3)(4). 2DHHA in n-dodecane were found to be 1.43 and 3.62, respectively. At high nitric acid concentration (>5 M), the amide undergoes protonation and extracts U(VI) and Pu(IV) as ion pairs of the type (UO2(NO3)(3)(-))(HDHHA(+)) and (Pu(NO3)(6)(2-))(HDHHA(+))(2). At trace level concentrations, the distribution coefficient (D) of Pu(IV) and U(VI) with a 1 M solution of DHHA in n-dodecane at 3.5 M HNO3 are 41.2 and 13.5, respectively. Similarly, at 50% uranium saturation of the organic phase the D values of Pu(IV) and U(VI) are 9.2 and 4.2, respectively. These results suggest the distinct advantages of DHHA over TBP in improved extraction of Pu and ease of stripping of uranium. The separation factors for 0.5 M DHHA at 30 Mrad are obtained as similar to 37 (U/Zr) and similar to 75 (Pu/Zr), suggesting that this extractant is particularly promising for the selectivity of Pu and U over Zr from irradiated solutions as compared to TBP. Results obtained during this work demonstrate the potential of amides in meeting the challenges posed by the large Pu content and high radiation fields encountered during the reprocessing of Pu-based fuels discharged from thermal as well as fast power reactors.