TRUEX flowsheet development as applied to ICPP sodium-bearing waste using centrifugal contactors

Abstract

Previous lab-scale work using batch contacts with sodium- bearing waste (SEW) simulant and samples of radioactive SEW from tank WM-185 suggested a potential flowsheet for partitioning actinides using solvent extraction (the TRUEX process). The suggested baseline flowsheet includes: an extraction section to remove actinides from liquid SEW into the TRUEX solvent (0.2 M CMP01 1.4 M TBP in Isopar-L); a dilute nitric acid scrub (0.07- 0.2 M HNO{sub 3}) to back extract co-extracted matrix materials (primarily Fe, Zr, and HNO{sub 3}) from the loaded solvent; thermally unstable complexants (TUCS) to back extract actinides; and a carbonate wash section for solvent cleanup. The purpose of the flowsheet development studies was to test and develop the baseline TRUEX flowsheet for ICPP SEW under continuous, countercurrent conditions using centrifugal contactors. All testing was performed using non-radioactive SEW simulant. Potential flowsheets were evaluated with regards to the behavior of the non-radioactive components known to be extracted by the TRUEX solvent. In general, the behavior of the individual components closely paralleled that anticipated from batch testing. The results indicate that eight extraction stages are more than sufficient to reduce the actinide content in the SEW to levels well below the NRC Class A LLW criteriamore » of 10 nCi/g. Iron was effectively scrubbed from the organic and 5% ended up in the high-activity waste (HAW) fraction. Zirconium scrubbing was not as effective and as much as 60% of the Zr in the feed could end up in the HAW fraction. The TUCS strip was effective at quantitatively stripping all metals except mercury from the TRUEX solvent. Carbonate washing effectively back extracted mercury from the stripped solvent, resulting in 99.4% of the mercury selectively partitioned from the SEW. « less

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