## 1 Introduction  
In the CANDU nuclear power plant, pressure tubes are made from Zr-2.5%Nb alloy with the following dimensions: a length of 6.4 m, an inner diameter of 0.104 m, and a wall thickness of approximately 4.2 mm. In normal conditions, the internal coolant has 10 MPa of pressure, and the temperature ranges between 260 \({}^{\circ}\)C at the D\({}_{2}\)O agent's entrance and 310 \({}^{\circ}\)C at the coolant's outlet at the opposite end of the pressure tube. The hard impurities trapped between the fuel bundle-bearing pad and the pressure tube, forming marks (volumetric flaws) on the inner surface of the pressure tube, are constantly connected to the fuel bundles even when the pressure tube is moving, which happens during the refueling process [1]. Based on operating experience with pressure tubes, it was found that some inspected tubes had faults that exceeded the permitted limits; of these, many were caused by hard contaminants that came into contact with the fuel-bearing pad or pressure tube. In the Zr-2.5%Nb alloy CANDU pressure tube, zirconium hydride platelets form when the equivalent hydrogen concentration is above the solid solubility limit. These are delta hydrides (ZrH\({}_{1.6}\)), which arise from mechanical and thermal stress conditions during regular CANDU fuel channel operation [2; 3]. It is important to remember that the hydride front that forms in the material when coolant enters the pressure tube will travel toward the mandrel area's high-stress locations due to the mechanical stress gradient [4]. The changes caused by hydrogen precipitation in zirconium alloys have been previously modeled using finite elements in the specialized literature. Numerous profile articles, particularly those concerning zirconium alloys, which are crucial for nuclear energy, have examined the impact of mechanical stress on hydrogen solubility [5; 6]. The zirconium matrix experiences a certain degree of brittleness as a result of the brittleness of the hydride platelets. As a result, part of the material's initial ductility and fracture resistance is lost. The degree of material fragility in the case of hydride platelet formation should be noted in light of the possibility of the platelets' reorientation under specific thermo-mechanical conditions (thermal cycling under continuous mechanical stress) [7; 8; 9]. When zirconium hydride platelets reach critical conditions, which are related to their size and the stress intensity factor \(K_{I}\), they fracture, and the cracks extend through the adjacent brittle hydride filaments in the pressure tube wall until they are stopped in the ductile matrix of the Zr-2.5%Nb alloy [6; 10; 11]. These features of the morphology of zirconium hydride platelets and their impact on crack initiation and propagation have been described by several microstructural parameters in the pertinent scientific literature [12]. Several measures, often referred to as metrics, have been defined in the scientific literature to quantify and characterize the morphology of zirconium hydrides in the material volume and to describe their impact on crack initiation and propagation, such as the total hydrogen content, zirconium hydride volume fraction [13], radial hydride fraction (RHF) [14], hydride continuity coefficient (HCC) [15], radial hydride continuity factor (RHCF) [16], and radial hydride continuous path (RHCP) [12]. It should be noted that all of the metrics defined above address uniform reorientation according to zircaloy-4 sheath thickness or pressure tube thickness. These metrics are less applicable for hydride reorientation zones located at the tips of volumetric flaws on a pressure tube, where the reorientation zone has a specific shape. These hydride reorientation zones located at the volumetric flaws on the Zr-2.5%Nb alloy CANDU pressure tube are rather circular, with a radius approximately corresponding to the defect depth in the radial direction.