Comparison of Actinides Separation by Coprecipitation and Chromatographic Resin (Dipex®) for Gross Alpha Determination

The determination of gross alpha in wastes that have alpha, beta and gamma emitters is important from a regulatory point of view. The level of alpha radioactivity allowed is limited in a low and medium level radioactive location for safety reasons, so it is necessary to measure it with high precision. In order to quantify the concentration of alpha emitters it is necessary to perform an adequate radiochemical separation before measurement. In this paper has been studied and compared the results obtained by two separation methods: one by coprecipitation using BaSO₄, Fe(OH)₃ and/or CaC₂O₄ as precipitant agents and the other one by extraction chromatography using Actinide Resin (Dipex®). The separation procedures have been applied to spent ion exchange resins from Spanish Nuclear Power Plants. Once the sample was dissolved by acid digestion in a closed vessel microwave equipment, and the radionuclides of interest were isolated of the rest by the techniques before mentioned, the gross alpha was measured by Liquid Scintillation Counting (LSC), using the α/β discrimination if necessary (when the separation was not completed), since this technique is today one of the most used and accurate for measuring radioactivity because LS spectrometry can detect practically all types of radiation with high efficiency.