[en] An accurate model for defining cladding deformation is required when performing fuel rod performance analyses. Cladding deformation models are used in cladding ovalization analysis as well as general fuel pin analyses of fuel temperatures, fission gas release, pin pressures, etc. Accurate creep models also are required to analyze the transient multi-axial stress histories which develop in the fuel rod cladding during Pellet Cladding Interaction. Of particular interest for normal operation analysis is the deformation resulting from cladding creep and irradiation growth. The development of these models and their correlation with operating data are discussed