No abstract

The oxidation studies of a sulfur to a sulfate ion by various oxyhalide oxidants in organic (thiourea, methionine) and inorganic (sulfate, thiophosphate) compounds were carried out in an acidic solution. The optimized result of the oxidation reaction was obtained when a bromate compound (BrO3−) as an oxidant and a 3 M HNO3 solvent. The chemical yield for the oxidation of the organic and inorganic sulfur compounds to a sulfate ion was monitored as 80% for thiophosphate, 87% for methionine, and 100% for thiourea and sulfate within 5% RSD. The oxidation of thiourea required at least 1.6 equivalents of the bromate in an acidic solution. In the case of the oxidation of methionine and thiophosphate, the oxidation yield was above 80% if the bromate was used at 20 times that of the substrates. The chemical yield in the paper sample (WypAll) exceeded 100% because of its background sulfur contents (910 ppm). The sulfate ion was quantitatively measured by using GPC and/or LSC counting of 35S followed by precipitates of BaSO4. The interfering nuclides (14C, 32P) were removed in an acidic condition. The minimum detectable activity (MDA) of 35S was found to be 0.1 Bq/g.

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.