Delayed hydride cracking of zirconium alloys

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Delayed hydride cracking (DHC) is a failure mechanism of certain metals in which hydrogen precipitating as brittle hydride leads to cracking of the metal. This is a particular problem for zirconium alloys that are used as pressure boundaries and radioactivity boundaries in nuclear reactors. When failure of these boundaries occurs there are severe consequences for an operating nuclear reactor and also for the nuclear fuel, both during operation and later when the spent fuel is in long-term storage. Currently, safe operation with zirconium alloys is ensured by placing limits on operating conditions based on empirical data for a limited number of experimental conditions. Models of DHC were developed over the years with the hope of enabling predictions of DHC under a wider range of conditions than can be experimentally measured. In the last five years the models used to explain the rates of DHC developed in the 80s and 90s have been critically questioned, and very recently the applicant et al. have shown that existing models to predict DHC velocity are based on faulty concepts and wrong assumptions. In addition, the applicant et al. have introduced a new model for DHC velocity that has successfully been used to predict a broad spectrum of experimental results; this is unprecedented and exciting, and incorporates a better understanding of the underlying physics. The goal of this proposal is to deepen this understanding while testing and developing further this new predictive model of DHC velocity. A reliable robust physical model of DHC will lead to better predictions of failures of zirconium components and, thus, improved safety for operating nuclear reactors and spent nuclear fuel in long-term storage.