DEVELOPMENT AND TESTING OF SREX FLOWSHEETS FOR TREATMENT OF IDAHO CHEMICAL-PROCESSING PLANT SODIUM-BEARING WASTE USING CENTRIFUGAL CONTACTORS

Laboratory experimentation has indicated that the SREX process is effe ctive for partitioning Sr-90 from acidic radioactive waste solutions l ocated at the Idaho Chemical Processing Plant. A baseline flowsheet ha s been proposed for the treatment of sodium-bearing waste (SBW) which includes extraction of strontium from liquid SBW into the SREX solvent (0.15 (M) under bar 4',4' (5')-di-(tert-butyldicyclohexo)-18-crown-6 and 1.2 (M) under bar TBP in Isopar L(R)), a 0.01 (M) under bar nitric acid strip section to back-extract components from the loaded solvent , and a 2.0 (M) under bar HNO3 solvent acidification section to equili brate the solvent with HNO3 prior to recycle to the extraction section . The flowsheet was designed to provide a decontamination factor (DF) of >10(3) which will reduce the Sr-90 activity in the waste solution t o below the NRC Class A LLW limit of 0.04 Ci Sr-90/m(3). SREX flowshee t testing was performed using sixteen stages of 5.5-cm diameter centri fugal contactors. The behavior of stable Sr and other components which are potentially extracted by the SREX solvent were evaluated. Specifi cally, the behavior of the matrix components including Pb, K, Hg, Na, Ca, Zr, and Fe was studied. The described flowsheet achieved 99.98% Sr removal (DF=4250) with one cycle of SREX. Potassium and Zr were parti ally extracted into the SREX solvent with 35% and 21%, respectively, e xiting in the strip product. Sodium, Ca, and Fe were essentially inext ractable. Lead was determined to extract and accumulate in the SREX so lvent and in the strip section. As a result, a Pb precipitate formed i n the strip stages of the contactors. Mercury was also determined to e xtract and accumulate in the SREX solvent.