APPLICATION OF LSC FOR THE DETERMINATION OF SOME RADIONUCLIDES IN WASTE MATRICES FROM THE IGNALINA NPP

ABSTRACT. Liquid scintillation counting (LSC) with a Quantulus (Wallac) was used to determine 55Fe, 63Ni, 90Sr, 129I, and 241Pu in waste matrices from the Ignalina nuclear power plant (NPP) in Lithuania. Actual radioactive waste samples were destroyed by different techniques according to the character of the matrix. After digestion, the concentrations of existing sta-ble Fe, Ni, and Sr were measured in the original sample using an atomic absorption spectrometer (AAS) with a graphite atom-izer (standard deviation 5–10%). A modified combined radiochemical separation procedure was applied for simultaneously determining 63Ni, 55Fe, and 90Sr from a single sample aliquot. The effective analytical separation of these isotopes from other traces found in radioactive waste was achieved using the following methods. The basic procedure for Fe and Ni analysis con-sisted of ferric hydroxide coprecipitation, anion-exchange separation of Fe, and extraction chromatographic separation of Ni on the NiSpec column. Separation of Sr was based on the extraction chromatographic procedure on a SrSpec (Eichrom Tech-nologies, Inc.) column developed by Horwitz et al. (1991). An alkaline leaching method for analyzing 129I in solid matrix waste samples or an ion-exchange chromatography method for analyzing this radionuclide in water were combined with puri-fication by extraction into chloroform and back-extraction into the aqueous phase. 241Pu was determined after purification by liquid-liquid extraction of dissolved material electrodeposited for alpha spectrometry. One-mL samples, obtained by evapo-ration or dissolution containing 63Ni, 55Fe, 90Sr, and 129I, were transferred to LSC vials for mixing with either OptiPhase HiSafe 2 or OptiPhase HiSafe 3 (PerkinElmer, USA) cocktail. An external standard quench correction was applied for activit