Separation of fission produced 106Ru and 137Cs from aged uranium targets by sequential distillation and precipitation in nitrate media

Ruthenium-106 and 137Cs have been separated from thermal-neutron irradiated UO3 targets aged for ~2.5 years by distillation and surface interactions in nitrate media of controlled chemical composition. After digestion of the aged targets with their aluminum wrapper in 2M NaOH solution, nitric acid was added to complete dissolution of the formed residue. The prepared fission product solution was separated from 129I and 91.8% 106Ru by sequential distillation from 20% and 40% HNO3 solutions containing H2O2 and KMnO4, as oxidants, and by boiling for 4 and 2.5 hours, respectively. The recovery yield of 106Ru collected in 0.1M NaOH solution was ~68.2% with a radionuclidic purity of ³99.99%. Thereafter, the fission product solution was brought to pH 9.5 by addition of NaOH solution to precipitate Al(OH)3, MnO2, and Na2U2O7 which selectively retained the remaining fission products leaving, mainly, 137Cs in the supernatant solution. The recovery yield of 137Cs was ≥97.3% with ~99.75% radionuclidic purity. The gamma-ray emitter contaminants which could be detected and identified in the recovered 137Cs solution, were ~0.25% 134Cs and ~1.4 . 10-3% 152,155Eu.