A new model of grain growth kinetics in UO2 fuel pellets. Part 1: Grain growth kinetics controlled by grain face bubble migration

A new mechanism of the lenticular grain face bubble migration which controls the bubble mobility and determines the drag force exerted on the grain boundary, is developed. It is shown that besides a more complicated (so called 'lenticular') shape of grain face bubbles, the migration mechanism of these bubbles might be essentially different from the intragranular bubbles, owing to their specific location on and interaction with a grain boundary. The model is validated against tests on grain growth kinetics during steady irradiation exposure and during post-irradiation annealing of UO2 fuel samples, and allows explanation of a strong retarding effect of irradiation on the grain growth observed in these tests.