Extraction Behavior of Fission Products with Tri-n-butyl Phosphate by Countercurrent Multistage Extraction in a Uranium, Plutonium, and Neptunium Co-recovery System

Abstract

In an attempt to develop a simplified solvent extraction process for U, Pu, and Np co-recovery, three countercurrent experiments were carried out to evaluate the effect of the scrubbing solution on the decontamination of fission products (FPs) using a dissolver solution derived from the irradiated core fuel of fast reactor “JOYO”. In all the runs, Np was co-extracted with U and Pu using tri-n-butyl phosphate (TBP) at the extraction section by using high HNO3 concentration feed solution. Of all the FPs, the decontamination behavior of Zr and Tc varied with the HNO3 concentration of the scrubbing solutions. Zirconium and Tc were not decontaminated with a single scrub flow sheet, which caused the accumulation of Zr at the co-decontamination section. The decontamination factors (DFs) of Zr and Tc were 2.62 × 101 and 1.07 × 100 with flow sheet using 9 and 1 mol/dm3 HNO3 scrubbing solutions, respectively. On the other hand, their DFs increased to >7.68 × 101 and >7.52 × 100 with 2 and 10 mol/dm3 HNO3 scrubbing solutions, respectively. The experimental results indicate that it is necessary to first remove Zr from the loaded solvent with a low HNO3 concentration scrubbing solution and then decontaminate Tc using a high HNO3 concentration solution. Other FPs, such as Cs, were effectively decontaminated with DFs in the range of 105.