Modelling Transient Fission Product Release from UO2 Fuel

Abstract

The dominant fission gas release mechanisms in UO₂ fuel during a high temperature accident transient may not be different from those during normal steady-state operation. Rather, it is the kinetics of these release mechanisms which may be different during the accident transient, primarily as a result of conditions which are accident-scenario specific. At Ontario Hydro, a simple but phenomenological transient release model was developed on this basis. It considers diffusion and grain growth as the dominant transient release mechanisms. The effects on the release kinetics of on-power and off-power conditions, as well as heatup in steam and inert atmospheres are accounted for. Comparisons of the model predictions to test data indicate good agreement. In this paper, we present a brief description of the model. and compare its predictions to experiments. The implications of the model on the current understanding of transient fission gas release behaviour are also discussed.