Effect of boiling upon radiolysis of iodide solution

The effect of void fractions on oxidation of iodide ions was examined in γ-radiolysis of iodide solution. All hydrogen produced by radiolysis of water transferred to gas phase at void fractions of about 1 and 10% at 293 and 373 K, respectively. At these void fractions, iodide ions were oxidized to iodate ions during irradiation with iodide concentration below 10-5 mol/L. This indicated that the fraction of OH radicals reacted wit h iodide ions was increased with the void fractions, because the reactivity between OH radicals and hydrogen was decreased. Analytical model was developed based on chemical reactions and mass transfer. The reaction scheme was composed of 35 reactions for pure water system and 89 reactions for iodide solution system. The analytical model could estimate the experimental results within ±20% of experimental values. In summary: The effect of boiling on oxidation of iodide ions was examined in γ-radiolysis of iodide solution. The following conclusions were obtained for the radiolysis of iodide solution at temperature below 200 deg. C and pH range from 4 to 8 under boiling condition. The following equilibriums are important to determine the oxidation state of iodide ions. At high iodide concentrations, the equilibriums are shifted to the right and then iodide ions are stable in near natural solution. At low iodide concentrations, iodate ions are formed via HOI under irradiation. I2 + I- ↔ I3- HOI+I- ↔ I2 +OH- Under boiling conditions, the turning concentration of iodide ions is about 5 x 10-6 mol/L. This turning concentration is lowered without boiling, because the amount of OH radicals is decreased by reaction of hydrogen and OH radical. This indicates that boiling makes it easier to convert iodine to iodate ions. All hydrogen and oxygen produced by radiolysis transfer to gas phase at void fractions of about 1 and 10% at 293 and 373 K, respectively. Analytical model developed based on 124 chemical reactions and mass transfer. The analytical model can estimate the oxidation state of iodide ions and the amounts of hydrogen and oxygen produced by radiolysis of iodide solution. (authors)