Unlike phonon-boundary resistance at the interface of two dissimilar lattices, the phonon grain-boundary resistance AR(p,gb) is over an ultrathin atomic restructured region bounded by two identical lattices. Using nonequilibrium, classical molecular dynamic simulations on bicrystal UO2 over 300-1200 K, we predict that AR(p,gb) (i.e., phonon, grain mean free path) is independent of temperature and the grain boundary type (e.g., tilt, twist). We compare these predictions with existing analytical models and identify those which include the proper grain-boundary phonon scattering mechanisms. Also, using the same embedded-atom interatomic potential models, we predict the phonon dispersion, density of states and bulk thermal conductivity of UO2, and verify the predictions (comparing with available ab initio molecular dynamics and experimental results), under equilibrium and nonequilibrium simulations. (C) 2016 Elsevier Ltd. All rights reserved.