The decomposition of aqueous iodide solution induced by γ-radiolysis and exposure to temperatures up to 300 deg C

Measurements were made of I2 and IO3- formed when aqueous KI solutions were exposed to ambient and high temperature with and without γ-irradiation. Parameters varied were time, dose, dose-rate, KI concentration and the presence of air, boric acid and lithium hydroxide, to provide information for calculations on the form in which iodine released from fuel as CsI in a reactor accident might reach the environment. In general iodine was the chief product, whose formation was accompanied by a pH increase which in unbuffered solutions prevented further oxidation. The concentration of product I2 reached a saturation value with increasing dose or time. In alkaline buffered solution and neutral unbuffered solution in the absence of air iodide was not oxidised upon irradiation. In neutral and buffered acidic solutions the maximum extent of I2 formation depended on the prevailing pH, from ca. 0.1% conversion of I- for unbuffered air saturated 10-1 M KI, to ca. 8% for buffered 10-3 M KI solution, pH 5.3 to 6.0. In acidic buffered solutions the extent of oxidation was independent of the presence of air. Results are discussed in terms of thermal and radiolytic kinetic and equilibrium data. (author)