Grain Growth Kinetics of UO_2-x Fuel Pellet

Grain growth kinetics of the substoichiometric UO_2-x fuel pellets were studied with constant heating speed and isothermal sintering experiments. Substoichiometric UO2-x fuel pellets can be fabricated with qualified density of 94.91%TD-96.23%TD (TD is theory density) and O and U atomic ratio of 1.975-1.990 when the mixed powders of UO_2+x and 5%U are sintered. Grain growth rate is very low when sintering temperature is below 1 650 ℃, but higher above 1750 ℃. It is found that the starting grain size G₀ cannot be neglected and the grain growth kinetics equation of the substoichiometric UO2-x fuel pellets is G⁴-G⁴₀=k0texp(-1 000Q/RT), resulting in grain growth feature exponent n=4, rate constant k0=78.76 μm4/h and activation energy Q=433.35 kJ/mol.