Delayed Hydride Cracking (DHC) of zirconium alloys has led to several failures of components in nuclear reactors and chemical plants. The process requires hydrides to form, and hence any understanding requires knowledge of hydride precipitation temperatures. Generally, these temperatures are determined using experimental techniques that do not involve cracking; hence, there is some ambiguity in relating these temperatures to cracking. With the advent of more precise cracking experiments, it is now possible to determine precipitation temperatures directly from cracking velocity measurements. In this study, precipitation temperatures were determined from crack velocity measurements, and compared with values determined from Differential Scanning Calorimetry (DSC), which form the basis of current standards. It was found that DSC onset temperatures provide the best indication of the precipitation temperature. In addition, the Diffusion First Model for DHC velocity is shown to provide better predictions, over a wide range of concentrations and temperatures, when the temperature in the standard TSSP equation is shifted to the onset temperature.
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