In this work, we quantify the impact of grain boundary (GB) and surface
diffusion on fission gas bubble evolution and fission gas release in UO2​
nuclear fuel using simulations with a hybrid phase field/cluster dynamics
model. We begin with a comprehensive literature review of uranium vacancy and
xenon atom diffusivity in UO2​ through the bulk, along GBs, and along
surfaces. In our model we represent fast GB and surface diffusion using a
heterogeneous diffusivity that is a function of the order parameters that
represent bubbles and grains. We find that the GB diffusivity directly impacts
the rate of gas release via GB transport, and that the GB diffusivity is likely
below 104 times the lower value from Olander and van Uffelen (2001). We also
find that the surface diffusivity impacts bubble coalescence and mobility, and
that the bubble surface diffusivity is likely below 10−4 times the value
from Zhou and Olander (1984).Comment: 34 pages, 11 figures, submitted at Journal of Nuclear Materials
(Under Review