Experiments to determine the oxidation rate, particle size distribution of oxide and release of iodine-131 from one kilogram, trace irradiated uranium slugs oxidizing at temperatures up to 1000°C in air and carbon dioxide are described. The release of iodine as a result of rapid melting of uranium is also investigated. It is concluded that extensive release of elemental iodine as vapour is always accompanied by extensive oxidation and that for temperatures below the melting point the release of elemental iodine as vapour is greater for oxidation in air than in carbon dioxide. It is stressed that for the geometrical arrangement and gas velocities used the greater part of the iodine inventory of the uranium remains contained in or adsorbed on particles of uranium oxide.