Determination of ⁹⁹Tc in TBP phase in spent nuclear fuel reprocessing with plastic scintillation resin

Technetium-99 is a major radionuclide affecting the separation of uranium, plutonium and neptunium in the PUREX process of spent fuel reprocessing due to its strong redox feature. The rapid and reliable determination of ⁹⁹Tc in TBP is very challenging, mainly due to the complexity of the sample matrix and the severe interference of radionuclides.

A rapid analytical method for the accurate determination of ⁹⁹Tc in TBP organic phase was developed in this work. ⁹⁹Tc was first back-extracted from TBP phase using a mixture of deionized water and carbon tetrachloride with an efficiency of 94.7 %, enabling to directly load to the plastic scintillation resin (TK-TcScint resin). ⁹⁹Tc adsorbed on the TK-TcScint resin was then directly measured by liquid scintillation counting (LSC). Importantly, the quenching correction for the counting efficiency of ⁹⁹Tc on the TK-TcScint resin was established for the first time. The excellent decontamination factors for all interferences (>10⁵) in the spent fuel solution (e.g., Sr, Cs, Sm, Fe, Zr, Ru, U) were achieved. The minimum detectable activity for ⁹⁹Tc in TBP phase was estimated to be 0.09 Bq/L with a counting time of 1 h, and the whole analytical procedure takes only about 2 h per batch of 12 samples.

This rapid and reliable analytical method is crucial to monitor ⁹⁹Tc in the TBP organic phase for the improvement of uranium-plutonium separation in the PUREX process. More importantly, the method with integrative separation and measurement analysis would be conducted for fully automated separation and measurement of ⁹⁹Tc in spent fuel reprocessing.