Radiolytic Degradation of Uranyl-Loaded Tributyl Phosphate by High and Low LET Radiation

Understanding and characterizing the radiolytic degradation of solvents used for treatment of used nuclear fuel is an ongoing topic of research. In the work presented here, degradation constants for the radiolysis of tributyl phosphate (TBP) as a function of various process variables, such as the inclusion of nitric acid and uranyl ions on the TBP, were determined. Degradation constants were determined for both high linear energy transfer (LET) and low LET (gamma) radiation exposure. Results indicate that susceptibility to gamma radiolysis is roughly twice that of high LET and that acid uptake by TBP has little effect on the overall degradation for both high and low LET irradiations. The inclusion of a metal ion affects the degradation of TBP by forming complexes that absorb a portion of the energy deposited by radiation. These TBP–metal complexes break down during irradiation, and the degradation constants for the complex were found to be higher compared to free TBP, for both high and low LET radiations suggesting that the TBP–uranyl complex is more susceptible to radiation than free TBP.