Integrated AMP-PAN, TRUEX, and SREX Flowsheet Test to Remove Cesium, SurrogateActinide Elements, and Strontium from INEEL Tank Waste Using Sorbent Columns and Centrifugal Contactors

摘要

Three unit operations for the removal of selected fission products, actinides,and RCRA metals (mercury and lead) have been successfully integrated and tested for extended run times with simulated INEEL acidic tank waste. The unit operations were ion exchange for Cs removal, followed by TRUEX solvent extraction for Eu (actinide surrogate), Hg, and Re (Tc surrogate) removal, and subsequent SREX solvent extraction for Sr and Pb removal. Approximately 45 L of simulated INTEC tank waste was first processed through three ion exchange columns in series for selective Cs removal. The columns were packed with a composite ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) sorbent. The experimental breakthrough data were in excellent agreement with modeling predictions based on data obtained with much smaller columns. The third column (220 cm3) was used for polishing and Cs removal after breakthrough of the up-stream columns. The Cs removal was in the ion exchange system without interference from other species. Most of the effluent from the ion exchange (IX) system was immediately processed through a TRUEX solvent extraction flowsheet to remove europium (americium surrogate), mercury and rhenium (technetium surrogate) from the simulated waste. The TRUEX flowsheet test was performed utilizing 23 stages of 3.3-cm centrifugal contactors. Greater than 99.999% of the Eu, 96.3% of the Hg, and 56% of the Re were extracted from the simulated feed and recovered in the strip and wash streams. Over the course of the test, there was no detectable build-up of any components in the TRUEX solvent. The raffinate from the TRUEX test was stored and subsequently processed several weeks later through a SREX solvent extraction flowsheet to remove strontium, lead, and Re (Tc surrogate) from the simulated waste. The SREX flowsheet test was performed using the same centrifugal contactors used in the TRUEX test after reconfiguration and the addition of three stages. Approximately 99.9% of the Sr, 99.89% of the Pb, and 96.4% of the Re were extracted from the aqueous feed to the SREX flowsheet and recovered in the strip and wash sections. Approximately 41 L of simulated tank waste (based on the volume processed through the TRUEX flowsheet) was processed through the integrated flowsheet and resulted in 175 L of liquid high activity waste (HAW) and 219.6 L of liquid low activity waste (LAW). The HAW fraction would be evaporated, dried and subsequently vitrified for final disposal. Based on current baseline assumptions, including a maximum phosphate loading of 2.5 wt. % in the HAW glass, the flowsheet tested would result in the production 0.195 kg of glass per L of tank waste processed. The LAW fraction would be solidified (via evaporation and denitration) and subsequently grouted. The current baseline assumptions for grouting the LAW stream indicate 0.37 kg of grout would be produced per L of tank waste treated. Under these assumptions, treating the current inventory of (approximately)5 E+6 L (5,000 m3) of tank waste would result in 375 m3 of HAW glass and 1,135 m3 of LAW Class A performance grout. The HAW glass volume could be significantly decreased by suitable TRUEX flowsheet modifications.