Simulations of coupled heat transport, oxygen diffusion, and thermal expansion in UO2 nuclear fuel elements

We study the coupled thermal transport, oxygen diffusion, and thermal expansion of a typical nuclear fuel element consisting of UO2+x fuel and stainless-steel cladding. Models of thermal, mechanical and chemical properties of the materials are used in a series of finite-element simulations to study the effect of the coupled phenomena on the temperature profile, oxygen distribution and radial deformation of the fuel element. The simulations include steady-state and time-dependent regimes in a variety of initial- and boundary value conditions that include sudden changes in the power density, variable oxygen content in the atmosphere, and variable temperature of the coolant. The study reveals the difference in the characteristic times associated with these phenomena and the importance of performing coupled simulations.