Assessment of fuel rod performance codes under ramp scenarios investigated within the SCIP project

The behavior of advanced cladding materials under challenging conditions needs to be fully characterized, understood and modeled. This paper assesses the current predictability of fuel performance codes under loadings expected from pellet–clad mechanical interactions. A set of scenarios experimentally characterized within the SCIP project, were chosen so that a variety of materials and ramp power sequences could be examined. odes have been used in this study: ALCYONE V1.1, FALCON-PSI, FRAPCON-3 v3.3 and STAV7.3. Their predictions have been compared to data in terms of cladding oxidation, diameters and elongation. Predictability of clad oxidation was certainly scattered and while some codes showed reasonable accuracy, other results were notably deviated. As for diameters, most of the codes were capable of qualitatively capturing the axial profile, and showed consistency between diameters and hoop stress and strain predictions. Elongation estimates were generally poor, and were rather far from measurements in most cases (even the trends observed just vaguely followed by the codes). sults reported have been discussed in the light of the set of individual hypotheses and approximations made by modelers and codes regarding both boundary conditions (i.e., power histories, inlet coolant temperature, refabrication, etc.) and fuel and clad characterization (i.e., densification, rim porosity, materials properties, etc.). Additionally, code-to-code comparisons of some key variables (i.e., fuel temperature, contact pressure, hoop and axial stresses, etc.) highlighted systematic tendencies of the codes and supported the observations made.