Demonstration of an Optimized TRUEX Flowsheet for Partitioning of Actinides from Actual ICPP Sodium- Bearing Waste Using Centrifugal Contactors in a Shielded Cell Facility

The TRUEX process is being evaluated at the Idaho Chemical Processing Plant (ICPP) for the separation of the actinides from acidic radioactive wastes stored at the ICPP. These efforts have culminated in recent demonstrations of the TRUEX process with actual tank waste. The first demonstration was performed in 1996 using 24 stages of 2-cm diameter centrifugal contactors and waste from tank WM183. Based on the results of this flowsheet demonstration, the flowsheet was optimized and a second flowsheet demonstration was performed. This test also was performed using 2-cm diameter centrifugal contactors and waste from tank WM1 83. However the total number of contactor stages was reduced from 24 to 20. Also, the concentration of HEDPA in the strip solution was reduced from 0.04 Mto 0.01 Min order to minimize the amount of phosphate in the HLW fraction, which would be immobilized into a glass waste form. This flowsheet demonstration was performed using centrifiigal contactors installed in the shielded hot cell at the ICPP Remote Analytical Laboratory. The flowsheet tested consisted of six extraction stages, four scrub stages, six strip stages, two solvent wash stages, and two acid rinse stages. An overall removal efficiency of 99.79% was obtained for the actinides. As a result, the activity of the actinides was reduced from 540 nCi/g in the feed to 0.90 nCi/g in the aqueous raffinate, which is well below the NRC Class A LLW requirement of 10 nCi/g for non-TRU waste. Removal efYiciencies of 99.84%, 99.97%, 99.97%, 99.85%, and 99.76% were obtained for 241Am, 238Pu, 239Pu, 235U, and 238U, respectively. Iron was effectively scrubbed from the TRUEX solvent, resulting in only 0.7% of the Fe exiting in the strip product. Mercury was extracted by the TRUEX solvent (74%) and stripped from the solvent in the 0.25 MNa,C03 wash section. Only 0.45% of the Hg exited with the high-activity waste strip product. The 0.01 MHEDPA strip section backextracted 99.4% of the actinide activity from the TRUEX solvent. However, poor material balances for the actinides, combined with the slight amount of precipitate observed when the stage 11 (strip product) solution was reequilibrated after shutdown, indicate that a precipitate formed in the strip section during operation. It is expected that this precipitate can be eliminated with a small adjustment of the HEDPA concentration and/or flowrate in the strip section.