Determination of ⁷⁹Se using a volatilisation method and liquid scintillation spectrometry

Highlights: • The presence of HBr was important for the distillation of the selenium. • The highest selenium recoveries were achieved in the mixture of 6.5 HCl /18.3. • The method was applied for the determination of ⁷⁹Se in radioactive wastes from nuclear power plants. - Abstract: The operation of nuclear power plants generates large quantities of radioactive materials or waste, which need to be characterised before decommissioning or for final disposal in radioactive waste repositories. The nuclear operators in Slovakia must declare 19 critical radionuclides in all radioactive waste before storage in the regional waste repository. This article describes a simple and rapid method for the determination of one critical radionuclide, ⁷⁹Se, in radioactive waste. The conditions for the effective distillation of selenium from various mixtures of HCl and HBr solutions were studied. The highest selenium recoveries were achieved in a mixture of 6.5 mol L⁻¹ HCl and 18.3 mol L⁻¹ HBr in 7:1 vol ratio. The method was applied for the determination of ⁷⁹Se in radioactive concentrates and sludge samples from nuclear power plants in Slovakia. ⁷⁹Se was measured with a TRI CARB 3100 TR liquid scintillation counter.