Estimation of effective thermal conductivity in U-10Mo fuels with distributed xenon gas bubbles

Abstract

We simulate the influence of distributed xenon gas bubbles on the effective thermal conductivity of irradiated U-10Mo fuel using a two-dimensional finite element method (FEM). The effective thermal conductivity of the inhomogeneous materials is estimated by solving the heat equation on a two-dimensional domain and estimating the mean temperature and heat flux. Bubble size distributions representative of both intra- and inter-granular fission gas bubbles are simulated. A distribution consistent with a gas bubble superlattice is compared to less-ordered bubble distributions in the intra-granular case. For inter-granular bubbles, the bubbles' spatial and size distribution was estimated from a two-dimensional scanning electron microscopy (SEM) image of fission gas bubbles that had collected on grain boundaries. The obtained results are compared with some theoretical models and experimental results. The results indicate that the pressure inside the bubbles has minimal influence on the overall thermal conductivity. The effect of krypton concentration is also negligible compared to pure xenon bubbles. Bubble arrangement is also insignificant unless a relatively wide bubble-free path through the metal exists. However, the area fraction of xenon bubbles has a significant impact on the overall thermal conductivity.