Phase-field simulation of fission bubbles formation in composite ceramic nuclear fuel

A phase-field model was developed to simulate the evolution of fission bubbles in UN-UO2 composite ceramic nuclear fuel. The model was firstly used to simulate the formation of UO2 intracrystalline bubbles, and the change of porosity obtained from the simulation was compared with the experimental data. The bubble evolution of UN-UO2 composite fuels in the UN and UO2 phase regions was then investigated for different burnups and doping concentrations. It was found that the nucleation rate of bubbles in the UN phase was slower than that in the UO2 phase, but the growth rate of bubbles in the UN phase was faster, so that the bubbles in the UO2 phase had a larger number density at low fuel consumption. It is specifically analyzed how the surface energy, diffusion coefficient and uranium density affect the difference in bubble evolution between the two phases.