Uncertainty improvement of ²²Na based radioactive tracer dilution for determining total mass of pyroprocessing molten salt systems by ¹⁵⁴Eu removal

To determine the total salt mass of the molten salt systems for pyroprocessing spent nuclear fuels, a ²²Na-based radioactive tracer dilution (RTD) technique was studied at Idaho National Laboratory in recent years. This ²²Na based RTD technique was deemed feasible, but due to the gamma energy peak of ²²Na coinciding with one of the energy peaks of ¹⁵⁴Eu, a common radioisotope in the molten salt, the uncertainty of the ²²Na radioactivity in the ²²Na-spiked salt samples was quite high. To improve the uncertainty of the ²²Na based RTD technique, we proposed using DGA resin to chemically remove the ¹⁵⁴Eu in the salt samples prior to gamma spectroscopy. The effectiveness of this approach in reducing uncertainty was evaluated. It was found that (1) the ¹⁵⁴Eu fission product effect on the uncertainty and detection limit can be effectively eliminated by chemically removing the ¹⁵⁴Eu during the salt sample preparation, and (2) the uncertainty of ²²Na radioactivity in the salt samples for electrorefining was significantly improved from 13 to 2%. This demonstrates the potential of practical engineering application of the ²²Na-based RTD as a safeguards method for molten salt systems for pyroprocessing spent nuclear fuels.