Distribution of Fission Products into Tributyl Phosphate under Applied Nuclear Fuel Recycling Conditions

Tributyl phosphate (TBP) is an important industrial extractant used in the Plutonium Uranium Redox Extraction (PUREX) process for recovering uranium and plutonium from used nuclear fuel. Distribution data have been assessed for a variety of fission and corrosion product trace metals at varying uranium concentrations under representative PUREX extraction (3 M HNO₃) and stripping (0.1 M HNO₃) conditions. As might have been anticipated, the extraction of most trace metals was found to decrease or remain constant with increasing uranium concentration. In contrast, the extraction of some low valence transition metals was found to increase with increasing uranium concentration. The increase in extraction of low valence transition metals may be related to TBP forming reverse micelles instead of recovering uranium as a classical UO₂(NO₃)₂(TBP)₂ coordination complex. The low valence transition metals may be being recovered into the cores of the reverse micelles. Also unanticipated was the lack of impact the TBP degradation product, dibutyl phosphate (DBP), had on the recovery of metals in batch distribution studies. This is possibly related to the batch contacts completed in these experiments not adequately recreating the multistage aspects of industrial-scale uranium extraction done using mixer settlers or centrifugal contactors