## 3 Results  
To better characterize the reorientation zone from the point of view of embrittlement and mechanical behavior, this paper proposes a novel metric for the morphology of hydrides located in the reorientation zone. Finite element analyses were performed on SENT specimens with flaws to evaluate the stress field around the notch tip (Figure 6(a)) to infer the stress concentrator factor \(K_{c}\). In the same picture, the principal stress graph is superimposed in front of the notch. The depth of the zone with stress greater than 120 MPa, that is, the threshold stress to start the reorientation process, was approximately 2 times the notch depth. In this sense, in the development of the model on which the novel metric is based, the characteristics specified in Figure 6(b) were taken into account. The circular area from the tip of the flaw was delimited, and it had a radius approximately equal to the depth of the defect, \(r\approx a\). This was also based on the hypothesis that at a distance equal to \(2a\) measured radially from the tip of the defect, the effect of stress concentration decreases, as demonstrated in Figures 1 and 6(a). Figure 5: Particular shape of the reorientation zone (RZ): (**a**) at the V-type notch flaw; (**b**) with the crack initiated by hydrides in the RZ; (**c**) with the crack crossing the RZ. Figure 6: Image analysis: (**a**) the RZ divided into 10 slices; (**b**) statistical data processing. Considering the cracking potential of the reorientation zone of localized hydrides, a novel metric is proposed for the hydride continuity coefficient in the reorientation zone, noted as \(\Phi_{\text{HCC(RZ)}}\). It is based on Figure 7b with the following considerations:  
7. The radius of the circular hydride reorientation zone located at the tip of a volumetric flaw in the wall of the CANDU pressure tube was approximately equal to the depth of the volumetric notch (r \(\approx\) a), taking into account the stress concentration at the tip of the defect. 8. All hydride filaments contained in the circular area of localized hydrides projected in the radial direction (Ox), and thus, a segment was constructed along the OX axis, a segment without discontinuities, \(LHCC1\), as shown in Figure 7b. The coefficient \(\text{HCC}_{\text{x}}\) in this area was \(\text{HCC}_{\text{x}}=1\). 9. The circle segment of the angle, \(\alpha^{0}\), was delimited, where \(\text{HCC}_{\text{x}}=1\), as denoted by the blue color in Figure 7b. 10. The novel metric \(\Phi_{\text{HCC(RZ)}}\) proposed for the \(\text{HCC}(\text{RZ})\) was defined as the ratio between the area of the circle segment defined by \(\text{HCC}_{\text{x}}=1\), as shown in Figure 7b, and the area of the circle with a radius equal to the depth of the defect (r \(\approx\) a), as follows:  
\[\Phi_{\text{HCC(RZ)}}=\frac{\pi\cdot\text{r}^{2}-\text{r}^{2}\Big{(}\frac{ \pi\cdot\alpha^{0}}{360^{0}}-\frac{\sin(\alpha^{0})}{2}\Big{)}}{\pi\cdot\text {r}^{2}} \tag{7}\]  
The value of the \(\Phi_{\text{HCC(RZ)}}\) metric better quantitatively defined the embrittlement of the area where the hydrides reoriented at the tips of volumetric defects on the Zr-2.5%Nb alloy CANDU pressure tube. Two examples of \(\Phi_{\text{HCC(RZ)}}\) metric calculation for samples with different hydrogen concentrations and flaw dimensions, which were subjected to various thermo-mechanical conditions, are displayed in Figure 8.  
Figure 7: (a) Principal stress field around the notch tip by FEA (unit = N/mm\({}^{2}\)); (b) characterization of the hydride reorientation zone (RZ) with the model HCC. To highlight the attributes of the novel \(\Phi_{HCC(RZ)}\) metric compared to the HCC metric, Table 1 lists the values of these metrics for the same evaluated samples, together with the values of the stress intensity factor, \(K_{I}\), and the volumetric flaw's tip stress concentration factor, \(K_{c}\).