CMP flowsheet development for the separation of actinides from ICPP sodium-bearing waste using centrifugal contactors

Previous results of lab-scale batch contacts with sodium-bearing waste (SBW) simulant suggested a potential flowsheet for partitioning actinides using solvent extraction with dihexyl-N,N-diethylcarbamoylmethyl phosphonate (DHDECMP or simply CMP) as the extractant. The suggested baseline flowsheet includes: an extraction section to remove actinides from liquid SBW into the CMP solvent (0.75 M CMP, 1.0 M TBP in Isopar-L{reg_sign}); a thermally unstable complexant (TUCS) strip section to back-extract actinides; a sodium carbonate wash section for solvent cleanup; and a dilute HNO{sub 3} rinse section to re-acidify the solvent. The purpose of these studies was to test and develop a baseline CMP flowsheet for Idaho Chemical Processing Plant (ICPP) SBW under continuous, countercurrent conditions using centrifugal contactors. This flowsheet was tested in two experiments using the Centrifugal Contactor Mockup which consists of sixteen stages of 5.5 cm diameter centrifugal contactors (procured from Oak Ridge National Laboratory). All testing was performed using non-radioactive SBW simulant. Potential flowsheets were evaluated with regard to the behavior of the non-radioactive components potentially extracted by the CMP solvent. Specifically, the behavior of the matrix components, including Fe, Hg, and Zr, was studied. In addition, Nd was added to the SBW simulant as a surrogate for {sup 241}Am. In general, the behavior of the individual components closely paralleled that anticipated from batch testing. Based on the assumption that the behavior of Am will be very similar to the behavior of the Nd surrogate, eight extraction stages are more than sufficient to reduce the actinide content in the SBW to levels well below the NRC Class A LLW criteria of 10 nCi/g. Very little Fe or Zr were extracted from the SBW simulant, resulting in only 1% of the Fe and 4% of the Zr exiting in the high-activity waste (HAW) fraction