Hydrogen concentration limit and critical temperatures for delayed hydride cracking in zirconium alloys

Experimental Results and Theoretical Interpretations of Solvus Relationships in the Zr–H System

“…Comparing this experimentally obtained value with 4 627 J/(mol H) (D" w el inc sphere ð ÞÀ " Q heat ¼ 4 178 À ðÀ449Þ J/(mol H) obtained from the accommodation energy model assuming a yield strength value of *500 MPa led Une and Ishimoto [45] to conclude that there was poor agreement between the hysteresis gap predictions obtained from the accommodation energy model compared to the value obtained experimentally. However, based on the revised experimentally determined enthalpy difference given by Shi et al [42], for the solvus data in Zr-2.5Nb, agreement between the predictions of the accommodation energy model and experimental results is now much closer. One would expect similar improved agreement to prevail for the Zircaloy-2 data obtained by Une and Ishimoto [45] when re-analyzed according to the approach of Shi et al [42].…”

“…However, based on the revised experimentally determined enthalpy difference given by Shi et al [42], for the solvus data in Zr-2.5Nb, agreement between the predictions of the accommodation energy model and experimental results is now much closer. One would expect similar improved agreement to prevail for the Zircaloy-2 data obtained by Une and Ishimoto [45] when re-analyzed according to the approach of Shi et al [42].…”

“…Details for determining this limit and the results obtained for unirradiated Zr-2.5Nb pressure tube material have been given by Shi et al [42]. A regression fit to these data, labeled DHCi, is included in Table 8.1 and plotted in Fig.…”

“…To obtain corresponding physically meaningful values from such fits to the data, the pre-exponentialsrepresenting all entropy contributions to the solvus other than entropy of mixingneed to be determined either from separate thermodynamic data or given a fixed value by choosing, for instance, a suitable average value of the pre-exponential terms obtained from the standard regression fits of the two solvi data sets. This was done by Shi et al [42] for the data obtained by Pan et al [31]. The enthalpy difference of 3 296 kJ/(mol K) calculated from the data of TSSP1 and TSSD for Zr-2.5Nb turned out to be much smaller than the value of 8 680 kJ/(mol K) obtained directly from the original regression fit by Pan et al [31].…”

Delayed Hydride Cracking: Theory and Experiment

“…A summary of most of the results of these studies is given in Shek's PhD dissertation [70]. 1 Experiments to determine this effect for pre-irradiated Zircaloy material were carried out by Schofield et al [67] who used the Dutton-Puls DHC growth rate model as applied by Shi et al [77] (described in the next section) to analyze these results, finding good agreement with the predictions of the model and the experimental results. A schematic representation of the dependence of the DHC rate on test temperature and direction of approach to test temperature, reproduced in Fig.…”