MARGARET: A comprehensive code for the description of fission gas behavior

The relevant phenomena concerning stable-fission gas behavior in nuclear fuels are combined in a single model: MARGARET. This same tool can be used for base irradiations up to high burnup, ramp tests and annealing tests. The representation of intragranular or intergranular bubbles and fabrication pores is highly mechanistic. The partition of fission gas between these cavities and dissolved in the solid permits determination of swelling of the fuel. The released gas is obtained by difference between the created and retained gas in the fuel. The model has been validated against base irradiations, ramps and annealing tests of UO2 fuel. The article presents the complete equations of the model in the base irradiation condition (Part I), followed by a detailed analysis of the behavior of a fuel irradiated up to 61 GWd/tU, extensively examined after irradiation (Part II). Part III presents the specific additional terms used for the calculation of transient and annealing conditions.