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 th e 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 extracti on 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), t he amide undergoes protonation and extracts U(VI) and Pu(IV) as ion pairs o f 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 ph ase the D values of Pu(IV) and U(VI) are 9.2 and 4.2, respectively. These r esults suggest the distinct advantages of DHHA over TBP in improved extract ion 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 (P u/Zr), suggesting that this extractant is particularly promising for the se lectivity of Pu and U over Zr from irradiated solutions as compared to TBP. Results obtained during this work demonstrate the potential of amides in m eeting the challenges posed by the large Pu content and high radiation fiel ds encountered during the reprocessing of Pu-based fuels discharged from th ermal as well as fast power reactors.