The loaded organic stream exiting the first extraction contactor is next subjected to the first scrubbing operation with a dilute HNO3 solution (dilute relative to the feed or ~2 M HNO3) to facilitate Zr and Ru removal from the organic phase. Other fission products that can be considered “entrained” versus “extracted”, such as Cs or Sr, are also removed from the organic phase in this step. The concentration of HNO3 must be judiciously chosen to prevent back extraction of U and Pu from the loaded solvent; however, the aqueous phase from the initial scrub potentially contains some uranium and plutonium, in addition to the scrubbed impurities, and is recombined with the incoming aqueous feed and returned to the extraction operation to minimize U and Pu losses.

Second scrub

The organic solvent emanating from the first scrub operation still contains the bulk of the Tc and Np that coextracted with the U and Pu. The organic is next subjected to a “technetium scrub,” where it is contacted with two scrub solutions containing different concentrations of HNO3. The first scrub with higher concentration nitric acid solution (10 M HNO3) effectively scrubs Tc from the organic phase (Baron 1993). The second scrub with a lower 1.5 M HNO3 solution essentially back extracts acid from the organic phase and limits the acidity of the organic exiting the system (Baron 1993).