Pore migration in UO2 and grain growth kinetics

Grain growth and density increase of UO2 has been measured during annealings at temperatures between 1650°C and 1750°C, for up to 300 h. The results have been compared to what can be deduced from a review of grain growth kinetics for undoped uranium dioxide. Although much theoretical and experimental work has been devoted to this topic, the mechanism controlling grain boundary migration cannot be clearly identified on the basis of available data. Since grain growth kinetics cannot be separated from pore migration, pore migration rates have been calculated using existing data for UO2 mass transport. In the temperature and pore size ranges investigated, it seems that surface diffusion is a more efficient mechanism for pore migration than evaporation–condensation (EC), although these results are strongly dependent on the reliability of the surface diffusion data.