LAUSR

Abstract Oxygen redistribution in UO2 fuel pellet occurring during reactor operation, where temperature gradient across pellet prevails, is modeled for steady state and transient situations. This phenomenon, called the Soret effect, is due to a positive shift of hyperstoichiometry in the fuel, i.e. from UO2 to UO2+x, and the prevailing temperature gradient during normal reactor operation. Unique solutions to the thermodiffusion equation for oxygen describing the phenomenon are found for various forms of the heat of transport during the steady state and under transient conditions. The solutions are used to compute radial oxygen profile across fuel pellet as per burnup. The relaxation time to thermal equilibrium during a transient is evaluated. This quantity depends on the oxygen diffusion coefficient and the eigenvalues of the putative equation, which are both a strong function of temperature.