The effect of temperature on radiolysis of iodide ion diluted aqueous solutions

In order to investigate the radiolysis of iodine containing aqueous solutions a flow type facility - Iodine Thermoradiation Facility (ITF) has been designed. It has a possibility to irradiate aqueous solutions in the steel vessel with 60Co γ-rays and continuously (on line) to analyze the products of radiolysis both in liquid and in gaseous phases. By means of ITF the formation of Iox (I2 + I3- + HOI), IO3-, H2O2 was studied in 10-5 - 10-3 mol/dm3 CsI aqueous solutions by their radiolysis at dose rate 4.5 kGv/h for six hours in region of temperatures from 313 to 404 K. Under similar conditions, some experiments in glass ampoules were also performed. The steady-state concentrations of Iox and IO3- decreased with increasing temperature as linear function of inverted temperature. The effect decreased with decreasing concentration of iodide ion. As the result, at high temperatures (T≥380 K) the steady-state concentration of Iox does not depend essentially on the iodide ion initial concentration. Molecular iodine (I2) released from the solution was the main radiolysis product in gaseous phase. Its steady-state concentration increased with increasing temperature because of iodine solubility in the water and decreased at the same time because the radiolytic iodine concentrations decreased. Therefore the most volatility of irradiated 10-3 and 10-4M CsI solutions was observed at the temperature about 350 K. The volatility of 10-5M solutions gradually decreased with increasing temperature. The experimental data were explained on the base of the hypothesis that the reaction between I2 and radiolytic H2O2 was the limit one determining the temperature dependence of Iox and IO3-steady-state concentrations. Its activation energy was estimated to be 27,5 kcal.mol-1. The temperature dependence for reaction (IO- + H2O2) was also estimated. (author) 8 figs., 1 tab., 17 refs