Decontamination of spent ion-exchange resins from the nuclear fuel cycle using chemical decontamination and direct current

The study presents the results of deep decontamination of the spent ion-exchange resin from the Kursk NPP, where the task of processing and conditioning of the resin is still not solved. The article shows that decontamination of the resin under dynamic conditions with a solution of the composition NaOH – 0.75 mol L−1, NaNO3 – 2.25 mol L−1 reduces its activity by 1 order of magnitude due to removal of Cs-137 (by washing). The subsequent washing of the resin with a solution of H2SO4 – 1.0 mol L−1, FeSO4 – 0.5 mol L−1 results in a decrease of its activity by another 1 order of magnitude due to removal of Eu-152-154 (100%) and partial removal of Co-60 (90%) and Am-241 (92%). It was found that further attempts to reduce the activity of the resin were ineffective due to the presence of insoluble precipitates, whose activity was mainly (more than 98%) accounted for by Co-60 (30.2%) and Nb-94 (68.1%) radionuclides. To remove these poorly soluble precipitates, we suggested decontamination by direct current through placing the resin between an anode and a cathode. A solution of H2SO4 of a concentration of 0.1 mol L−1 was used as an electrolyte. It has been found that an addition of FeSO4 (0.009 mol L−1) increases the rate of precipitate removal more than 1.5-fold. During the treatment by electric current, particles are mechanically removed, whereas insignificant amounts of Cs-137 and Co-60 (no more than 2.6%) enter the electrolyte. After the treatment and washing the resin with a NaNO3 solution, its activity decreases by another three orders of magnitude. The resulting activity of the resin was 350 Bq kg−1, which made it possible to classify it as industrial waste.