Transient failure of zircaloy cladding: State-of-the-art study and model development: Final report

A state of the art study of transient failure of zircaloy reveals that a wide range of failure models exist, and their use in fuel analysis depends upon the type of application. Licensing analyses, for example, employ highly simplified criteria that depict cladding rupture in terms of a single response variable, usually the nominal circumferential stress, as function of temperature; while fuel behavior analyses use more detailed models with varying levels of sophistication. Some of these models, however, are ill-suited for detailed fuel rod analysis computer codes because of their dependence on case-specific parameters; others are limited in their utility because of inherent deficiencies in their theoretical treatment of the phenomena involved. Based on this study, a new zircaloy transient failure model is developed that takes account of the important variables involved in transient phenomena, namely, heating rate, strain rate, temperature, true stress, true strain, and prior condition of the cladding material. The model is particularly suited for detailed fuel rod analysis and thus was implemented in the FREY code