Determination of ¹²⁵I and ¹³¹I in Radioisotope Wastes

In order to measure a low activity of ¹²⁵I and ¹³¹I in radioisotope wastes, we took into consideration various sample preparation and separation methods, such as an acid decomposition, an acid leaching and a combustion method. In a previous study, the maximum chemical yield of iodine by an acid leaching was found to be 78.0%. However, in this study, the maximum chemical yield of the acid decomposition method and the combustion method with a radioiodine reference solution was found to be 99.1% and 84.5%, respectively. We selected the acid decomposition method for the analysis of radioisotope waste samples due to its high chemical yield and short preparation and separation time. The chemical yield of the acid decomposition method depends on the reaction time at each experimental stage, added amount of H₃PO₃ and H₂O₂, and the pH of the condensed solution and the condition of the AgI precipitation. The important point for the highest recovery rate from a acid decomposition method is to maintain enough reaction time and pour 10 mL of 30% H₃PO₃ before a distillation, and drop 1 mL of H₂O₂ when the condensed solution is trapped in the Florence flask. Through a study of the acid decomposition method we found an optimal preparation and separation method of ¹²⁵I and ¹³¹I in radioisotope wastes due to the merits of a short reaction time and high recovery rate, and a counting system was applied to LEPS for the ¹²⁵I and HP Ge gamma-ray spectrometer for ¹³¹I.