ABSTRACT
Among the many radioactive fission products which may be released from reactor fuel during an accident sequence, iodine and cesium are commonly the ones of most immediate concern to the general public. For different accident sequences temperatures may range from close to operating values up to the melting point of UO2 and the chemical environment may vary from strongly reducing to highly oxidizing conditions. Oxidation of UO2 in both steam and air has been studied in the laboratory using unirradiated samples. The kinetics, as well as tests in dry air, supports the hypothesis that the volatile species is UO3 gas. Iodine release was measured in air at temperatures as low as 500°C. Cesium releases were not detected below 750°C. At higher temperatures the release percentages of iodine and cesium were similar. When steam was introduced the oxidation rate increased as did the cesium release rate. When the sample reached equilibrium stoichiometry, the cesium release rate dropped almost to zero.
