Direct simulation Monte Carlo study of phonon heat conduction in solid nuclear fuels

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Heat transfer in solid nonmetallic thin films can be best described by the phonon Boltzmann transport equation (BTE). In this study, the direct simulation Monte Carlo (DSMC) technique is used to solve the phonon BTE for thick and thin uranium dioxide (UO2) films. Phonon drift and collisions are simulated in separate time steps. The phonon distribution is simulated as a function of space, momentum, and time. A three-phonon collision model derived from time-dependent perturbation theory is used to simulate Normal and Umklapp scattering events, while obeying the energy and quasi-momentum conservation rules. Unlike in past Monte Carlo simulations of phonon heat conduction, this collision model does not require an overall relaxation-time approximation or a creation-destruction scheme to enforce energy conservation. This simulation method follows the time-evolution energy content of the film. The steady-state heat flux and temperature distribution are determined as functions of space and time and as moments of the phonon distribution. The simulation results show close agreement with known behavior in both the diffusion and ballistic regimes.