Meso-scale modeling of the influence of intergranular gas bubbles on effective thermal conductivity

Using a meso-scale modeling approach, we have investigated how intergranular fission gas bubbles, as observed in high-burn-up nuclear fuel, modify the effective thermal conductivity in a polycrystalline material. The calculations reveal that intergranular porosity has a significantly higher resistance to heat transfer compared to randomly-distributed porosity. A model is developed to describe this conductivity reduction that considers an effective grain boundary Kapitza resistance as a function of the fractional coverage of grain boundaries by bubbles.