Removal of silver and antimony radionuclides from low-level liquid radioactive waste of a research reactor through different scavenging precipitations

摘要

After upgrading the Pakistan Research Reactor-1, the amount of liquid waste and its increased radioactivity content necessitated a pre-disposal treatment to bring the activity down to disposal limits. Amongst several radionuclides in the waste, Ag-110 and to some extent Sb-124 were of our concern due to their higher production rate. Different possible treatment processes were considered for the treatment of low-salt, low-level liquid waste of the institute. Making use of insolubilities and scavenging properties of certain precipitates of metal ions, some experiments on the actual waste samples were performed for the decontamination of the piled up waste effluent. Suitable reagent(s) and the optimum doses were to be investigated for the treatment and conditioning of the wastewater. Different scavenging agents like ferric chloride, ferrous sulfate, stannous chloride, in situ precipitated manganese hydroxide and lanthanum nitrate were studied for the removal of these two radionuclides. Selectivity of Fe2+ and Fe3+ as scavengers for silver and antimony was investigated. Excellent Decontamination Factors (> 1000) were obtained very cost effectively with some of the reagents tried. Based on these experiments, a working procedure making use of Fe(II) hydrous oxide scavenging precipitation for the chemical treatment of the waste effluent was optimized. These experiments are presented.