Review of the thermodynamic basis for models of delayed hydride cracking rate in zirconium alloys

A review is given of the thermodynamic basis of a model developed by Dutton and Puls for the rate of subcritical crack propagation by delayed hydride cracking in zirconium alloys. This review was prompted, in part, by the publications of a series of recent papers by Kim and co-workers in which it is claimed that the thermodynamic basis of the Dutton and Puls model and its subsequent refinements is incorrect, prompting them to propose a new model. This review demonstrates the validity of the original model and shows the origin of the error made by Kim in claiming that the Dutton and Puls model was incorrectly formulated. It also explains the reasons why Kim’s new delayed hydride cracking model is incorrect. This review was further prompted by the author’s realization that the series of papers documenting the development of the various versions of the original Dutton and Puls model contain typographical errors, differences in sign convention, differences in input data, minor errors and/or changes in formal representation as well as occasional misleading, confusing or incorrect statements of the physical significance of the thermodynamic basis of the model. All of these shortcomings could have resulted in misunderstandings regarding the correct formulation of the model and the physical significance of the results. Therefore another important purpose of this review is to provide an updated treatment of the original version that puts all subsequent versions of the DHC model on a consistent thermodynamic basis.