Validation of Solvent Extraction Scheme for the Reprocessing of Advanced Heavy Water Reactor Spent Fuel Using N,N-Dihexyl Octanamide as Extractant

Even though tri-n-butyl phosphate (TBP) has been the work horse for spent fuel reprocessing, some of its drawbacks are of major concern. Based on batch extraction studies, our group at Radiochemistry Division, BARC has proposed N,N-dihexyl octanamide (DHOA) as an alternative extractant to TBP for the reprocessing of three component Advanced Heavy Water Reactor (AHWR) spent fuels. To validate the batch data, twelve stage counter-current mixer settler runs were carried out on a simulated AHWR feed [∼2 g/L U + ∼2 g/L Pu + 100 g/L Th + 0.03 M HF + 0.1 M Al(NO3)3 at ∼3.5 M HNO3] (with a Pu tracer instead of 2 g/L; due to marginal variation in its extraction behavior) with 0.18 M TBP and 0.36 M DHOA/n-dodecane as extractants. Quantitative extraction of Pu and U was achieved in ∼5 stages (maintaining volume ratio (O/A) as 1.1) leaving the bulk of thorium in the raffinate. Co-extracted thorium (∼4.5%) from the organic phase was scrubbed using 4 M HNO3. Partitioning of Pu from a loaded organic phase was carried out employing 0.5 M hydroxyl ammonium nitrate (HAN) at 2 M HNO3 as the strippant. Finally, uranium was stripped quantitatively using 0.01 M HNO3. The results clearly established the cocurrent studies using 0.36 M DHOA/n-dodecane as the extractant. The proposed flow sheet using 0.36 M DHOA/n-dodecane appears attractive with respect to the volume of the organic waste generated as compared to that of 0.18 M TBP/n-dodecane. Radiolytic degradation and hydrodynamic parameters of 0.36 M DHOA were also evaluated vis-à-vis 0.18 M TBP in n-dodecane.