Prediction of the UO2 fission gas release data of Bellamy and Rich using a model recently developed by combustion engineering

A model recently developed by Combustion Engineering, Inc. (C-E) for fission gas release from UO2 fuel recognizes the separate effects of temperature-dependent and temperature-independent release mechanisms. This model accounts for a moderate burnup enhancement that is based on the concept of a saturation inventory existing for the intra- and inter-granular storage of fission gas within the fuel pellet. The saturation inventory, as modeled, is strongly dependent on the local temperature and the changing grain size of the fuel with burnup. Although the fitting constants of the model were determined solely from more current gas release data from fuel more typical of the C-E product line, the model, nonetheless, provides an excellent prediction of the Bellamy and Rich data over the entire burnup range represented by the data (+- 1.6% gas release at a 1 σ level). The ability to obtain a good comparison with this data base provides additional support for the use of the particular separation of the effects of thermal diffusion and burnup enhancement on fission gas release that is embodied in the model. (author)