An advanced model for grain face diffusion transport in irradiated UO2 fuel. Part 1: Model formulation

An advanced model for the grain face transport of gas atoms, self-consistently taking into consideration the effects of atom diffusion over the grain surface, their trapping by and irradiation induced resolution from intergranular bubbles is presented. The model allows prediction of a noticeable gas release from UO2 fuel without visible interlinkage of grain face bubbles, i.e. at very low grain face coverage, below the critical value manifested by formation of bubble channels on grain faces interconnected with open porosity, in accordance with experimental observations of UO2 and MOX fuel behaviour under various irradiation conditions.