Unstable fission product release from UO2 irradiated at high temperature

A model of the release of unstable gaseous and volatile fission products from UO2 nuclear fuel during irradiation is developed. By considering the physical processes controlling the release of those atoms produced remote from the outer surface of the fuel an effective diffusion coefficient has been defined for the transport of the radioactive species along the partially connected grain-edge porosity. The magnitude of this coefficient is shown to be sensitively dependent upon the volume of grain-edge porosity and example calculations are discussed. (orig.)