Synopsis of the basic models implemented in the fuel rod behavior codes Frap-T and SSYST and some results of comparative calculations. Synopsis of the basic models implemented in the fuel behaviour codes Frap-T and SSYST and some results obtained

FRAP-T2 and SSYST-I are computer codes to predict the behavior of a single LWR fuel rod under accident conditions. This paper compares its programming and operational features, the computational models and the results obtained for a sample problem. The overall-results agree well: ballooning starts in both calculations at nearly the same time at the same place. A detailed comparison shows good agreement in the heat conduction and the clad-deformation models, a fairly good agreement in the gap pressure calculation and some differences in the gap heat transfer