Comparisons Between Measured and FRAP-T4-Predicted Fuel Rod Failure Probability Under Pellet-Cladding Interaction Conditions

The results of power ramp tests and associated cladding failure calculations performed as part of FRAP-T4 independent assessment studies have been analyzed. The 90 ramp tests considered are characterized in terms of relevant fuel design and operating parameters for Zircaloy-clad UO₂ fuel rods. The use of alternative gap closure and fuel deformation models strongly affects results of the current stress-dependent failure probability model. The influence of both mechanical and chemical failure mechanisms can be separated to some extent by interpreting the concurrent effects of both the ramp-induced stress levels and the relative amounts of retained fission gas available for promoting stress corrosion. A relatively simple modeling approach can meet the basic mechanistic requirements for calculating pellet-cladding interaction failure probability.