A flowsheet with selective stripping of Cs and Sr has been developed for partitioning HLW with long-lived (Cs-137 and Sr-90) and ultralong-lived (An) radionuclides into fractions. The flowsheet involves the following operations:

• Combined extraction of Cs, Sr, An and REE by a UNEX-extractant (11 stages).

• Scrubbing of the extract with a solution of 1 M HNO3 containing 0.03 M citric acid (1 stage).

• Combined stripping of Cs and Sr by a solution containing 1 M guanidine nitrate, 0.1 M HNO3 and 0.03 M citric acid (6 stages).

• Stripping of An and REE by a solution containing 1 M guanidine car­bonate, 0.2 M acetohydroxamic acid and 0.03 M DTPA (3 stages).

• Regeneration of the extractant by a 3 M HNO3 solution (5 stages).

This flowsheet (Fig. 9.5) was also tested at pilot plants with centrifugal contactors at RI and the Idaho National Laboratory.