Demonstration of a Universal Solvent Extraction Process for the Separation of Cesium and Strontium from Actual Acidic Tank Waste at the INEEL

A universal solvent extraction process is being evaluated for the simultaneous separation of Cs, Sr, and the actinides from acidic high-activity tank waste at the Idaho National Engineering and Environmental Laboratory (INEEL) with the goal of minimizing the high-activity waste volume to be disposed in a deep geological repository. The universal solvent extraction process is being developed as a collaborative effort between the INEEL and the Khlopin Radium Institute in St. Petersburg, Russia. The process was recently demonstrated at the INEEL using actual radioactive, acidic tank waste in 24 stages of 2-cm diameter centrifugal contactors located in a shielded cell facility. With this testing, removal efficiencies of 99.95%, 99.985%, and 95.2% were obtained for 137 Cs, 90 Sr, and total alpha, respectively. This is sufficient to reduce the activities of 137 Cs and 90 Sr to below NRC Class A LLW requirements. The total alpha removal efficiency was not sufficient to reduce the activity of the tank waste to below NRC Class A non-TRU requirements. The lower than expected removal efficiency for the actinides is due to loading of the Ph2Bu2CMPO in the universal solvent exiting the actinide strip section and entering the wash section resulted in the recycle of the actinides back to the extraction section. This recycle of the actinides contributed to the low removal efficiency. Significant amounts of the Zr (>97.7%), Ba (>87%), Pb (>98.5%), Fe (6.9%), Mo (19%), and K (17%) were also removed from the feed with the universal solvent extraction flowsheet