## 2 Materials and Methods
### Experiments for Zirconium Hydride Reorientation  
Processed around the pressure tube's ring, the Zr-2.5%Nb pressure tube alloy samples had a SENT shape, as shown in Figure 3. The specimen roughness was an as-received value for the pressure tube.  
An electrolytic bath containing a 0.1% H\({}_{2}\)SO\({}_{4}\) solution deposited the hydride layer on the raw samples. The polished Zr-2.5%Nb samples served as the cathode, while a 5 mm thick lead plate served as the anode. The current density used was 100 mA/cm\({}^{2}\). Eight hours were allotted for holding, and the working temperature was 90 \({}^{\circ}\)C in the electrolytic bath. After this treatment, a homogeneous layer of hydride was produced. This was followed by a thermal homogenization treatment, which caused hydrogen to diffuse throughout each sample's volume. The period of hydrogenation was determined to obtain the required final hydrogen concentration in the samples. The samples were heated for two hours at 425 \({}^{\circ}\)C in a vacuum chamber as part of the hydride heat treatment.  
To determine the hydrogen concentration in the samples, the \"ELEMENTRAC OH-p\" analyzer was used, which provided the measurement results directly in parts per million. The measuring principle of the ELEMENTRAC OH-p elemental analyzer allows a wide measuring range. To analyze each sample, it was weighed and placed on the sample port. The graphite crucible was outgassed in the impulse furnace of the analyzer to  
Figure 3: Single-edge notched tension-type sample: (**a**) dimensions in mm; (**b**) specimen.  
Figure 2: Single-edge notched tension-type sample [19].  
reduce possible contamination. For hydrogen analysis, a nitrogen carrier and a sample gas were passed through a Schuetze reagent. With an absolute inaccuracy of + / -5 ppm, the controlled hydrogen in the samples was within the range of 30-80 parts per million (ppm) in this work considering how the hydrogen concentrations in the pressure tubes of the CANDU reactor changed. Established metallographic procedures were applied to highlight the hydrides and ascertain their orientation. Specifically, the samples were polished and subjected to a chemical attack (a solution consisting of 45% nitric acid, 45% distilled water, and 10% hydrofluoric acid; t = 20 s). A particular chemical attack--immersion in a mixture of 25 mL of lactic acid, 25 mL of nitric acid, and 3 to 4 drops of hydrofluoric acid--was used to highlight the hydrides. The samples' microstructure was examined under a light field metallographic microscope. Certain heat cycling tests were carried out to acquire the hydride reorientation phenomenon. To enable a thermal cycling treatment under the controlled load of samples with artificial flaws, such as V-type flaws, an experimental setup was employed at the testing facility.  
Thermal cycling treatments under continuous mechanical load were used to observe the hydrides in the location of reorientation. The operating procedures were as follows:  
1. The instrumented and hydride samples were installed in the clamping mechanism typical of the SENT sample type;
2. The samples were heated to 300 \({}^{\circ}\)C for a full day to dissolve the hydrides. Subsequently, the temperature was lowered to 185 \({}^{\circ}\)C at a rate of 1 \({}^{\circ}\)C per minute, and the holding period was extended to three hours. Following this, the cooling process was maintained at a rate of 1 \({}^{\circ}\)C per minute until 90 \({}^{\circ}\)C was reached. Then, the samples were heated to 250 \({}^{\circ}\)C at a rate of 1 \({}^{\circ}\)C per minute for one hour.  
The parameters for testing were managed with the aid of appropriate software. The number of heating cycles under constant mechanical stress varied between 9 and 25. Based on initial experiments conducted on samples containing a hydrogen concentration greater than 30 ppm, the threshold stress for hydride reorientation was determined over a temperature range of 280 to 350 \({}^{\circ}\)C.