Feasibility studies on the detection of third phase formation in the solvent extraction equipment during reprocessing of fast reactor spent fuels

Abstract

Fast reactor spent fuel plants reprocess plutonium rich fuel discharged from fast reactors. Centrifugal extractor or mixer settler solvent extraction equipments are employed for the selective recovery of nuclear grade uranium and plutonium from fission products. 30% (v/v) TBP/NPH is used as the solvent in PUREX process. Plutonium rich spent fuel has disadvantage of third phase formation during process upsets. Third phase can leads to flooding thereby prone for nuclear criticality or explosion hazard in evaporators. Hence, the solvent extraction equipments should be continuously monitored to detect onset of third phase. Studies are carried out by placing electrical conductivity probe in the organic outlet of a single stage mixer settler. This study measured electrical conductivity in different runs. 12 M feed nitric acid run and 15.8 M nitric acid feed acidity run indicated the conductivity at organic outlet is beyond 1035 μS/cm, indicated severe flooding as well as two phases in organic collecting container. Uranous in nitric acid run indicated when the A/O change was initiated loaded organic phase (8–11 μS/cm) conductivity at organic outlet decrease to 2.06 μS/cm as well when probe inserted at the organic and aqueous interface jumped to 190 μS/by forming Third phase. The results of this study indicated it is feasible to detect online of third phase in solvent extraction equipment such as mixer settler.