Influence of Boric Acid in the Extraction of Uranium (VI), Plutonium (IV) and Europium (III) from Fast Reactor Fuel Dissolver Solution

Addition of boric acid to dissolver solution has been proposed for minimizing the criticality concern associated with reprocessing of fast reactor fuel. Extraction of uranium (VI) and plutonium (IV) from the resultant nitric acid – boric acid medium by a solution of tri-n-butyl phosphate (TBP) in n-dodecane (n-DD) has been studied at 298 K. The distribution ratios of uranium (VI) and plutonium (IV) were found to be comparable with those obtained in the absence of boric acid. Extraction of europium (III) from nitric acid – boric acid by a solution of 1.2 M TBP–0.2 M n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in n-DD was also studied. The solubility limit of boric acid as a function of nitric acid concentration was determined and it was found to decrease from 61.5 g/L in 0.1 M HNO3 to 32.4 g/L in 4 M HNO3 at 303 K. Extraction of boric acid in 1.1 M TBP/n-DD and in a solution of 1.2 M TBP–0.2 M CMPO in n-DD was studied and it was found to increase with increase in the concentration of boric acid above ~0.2 M. The study indicated that the interference of boric acid during the extraction of uranium (VI) plutonium (IV) by PUREX solvent and Eu(III) by TRUEX solvent was negligible and the added boric acid could be quantitatively retained in aqueous phase provided the boric acid concentration was fixed below 6 g/L (~0.1 M) in the feed solution.