**2. Experimental Procedures**

The Zircaloy-2 specimens were annealed at 630 ◦C for 2 h and subsequently air-cooled. Table 1 shows the results of the chemical analyses and the measurements of the hydrogen impurity levels of these specimens. The samples were irradiated at room temperature with 5.0–30 keV D<sup>2</sup> + ions and 3.2 MeV Ni3+ ions by an ion implanter and a tandem accelerator at Kyushu University. Figure 1a shows the ion irradiation chamber (with a duo-plasma ion gun) used for the D<sup>2</sup> + irradiation, and Figure 1b shows the specimen holder used for the D<sup>2</sup> <sup>+</sup> and Ni3+ ion irradiation. Figure 2a shows the depth profile of the damage rate, and Figure 2b shows the concentration of D<sup>2</sup> + ions irradiated at each accelerating voltage. The damage estimation was obtained from the Stopping and Range of Ions in Matter (SRIM) calculation [18], for which the threshold energy for displacement was assumed to be 40 eV. After irradiation at room temperature at a flux of 1.0 <sup>×</sup> <sup>10</sup><sup>18</sup> ions/m<sup>2</sup> s, the samples were transferred into the vacuum chamber of the TDS apparatus. After they were evacuated, the specimens were held at room temperature for a period of time (less than 2 h) and TDS measurements were conducted. During the heating, with a ramping rate of 1 ◦C/s up to 900 ◦C, the thermal desorption of HD (mass = 3) and D<sup>2</sup> + (mass = 4) were measured using quadrupole mass spectroscopy. The desorption rate was calibrated by a He standard leak and corrected the relative ionization efficiency. *Quantum Beam Sci.* **2021**, *5*, x FOR PEER REVIEW 2 of 10 In this study, 3.2 MeV Ni3+ ion irradiation is applied to Zircaloy-2 samples. The samples are injected with 5.0–30 keV D2+ ions to understand the trapping and de-trapping process of hydrogen on N3+ ion irradiated Zrycaloy-2. Thermal desorption spectroscopy (TDS) and conventional transmission electron microscopy (C-TEM) are conducted following the irradiation to evaluate the details of retention and desorption of the implanted deuterium and to identify the responsible traps. **2. Experimental Procedures**  The Zircaloy-2 specimens were annealed at 630 °C for 2 h and subsequently aircooled. Table 1 shows the results of the chemical analyses and the measurements of the hydrogen impurity levels of these specimens. The samples were irradiated at room temperature with 5.0–30 keV D2+ ions and 3.2 MeV Ni3+ ions by an ion implanter and a tandem accelerator at Kyushu University. Figure 1a shows the ion irradiation chamber (with a duo-plasma ion gun) used for the D2+ irradiation, and Figure 1b shows the specimen holder used for the D2+ and Ni3+ ion irradiation. Figure 2a shows the depth profile of the damage rate, and Figure 2b shows the concentration of D2+ ions irradiated at each accelerating voltage. The damage estimation was obtained from the Stopping and Range of Ions in Matter (SRIM) calculation [18], for which the threshold energy for displacement was *Quantum Beam Sci.* **2021**, *5*, x FOR PEER REVIEW 2 of 10 In this study, 3.2 MeV Ni3+ ion irradiation is applied to Zircaloy-2 samples. The samples are injected with 5.0–30 keV D2+ ions to understand the trapping and de-trapping process of hydrogen on N3+ ion irradiated Zrycaloy-2. Thermal desorption spectroscopy (TDS) and conventional transmission electron microscopy (C-TEM) are conducted following the irradiation to evaluate the details of retention and desorption of the implanted deuterium and to identify the responsible traps. **2. Experimental Procedures**  The Zircaloy-2 specimens were annealed at 630 °C for 2 h and subsequently aircooled. Table 1 shows the results of the chemical analyses and the measurements of the hydrogen impurity levels of these specimens. The samples were irradiated at room temperature with 5.0–30 keV D2+ ions and 3.2 MeV Ni3+ ions by an ion implanter and a tandem accelerator at Kyushu University. Figure 1a shows the ion irradiation chamber (with a duo-plasma ion gun) used for the D2+ irradiation, and Figure 1b shows the specimen holder used for the D2+ and Ni3+ ion irradiation. Figure 2a shows the depth profile of the damage rate, and Figure 2b shows the concentration of D2+ ions irradiated at each accelerating voltage. The damage estimation was obtained from the Stopping and Range of Ions in Matter (SRIM) calculation [18], for which the threshold energy for displacement was

> **Table 1.** Chemical composition of the materials used in the present study (wt%). assumed to be 40 eV. After irradiation at room temperature at a flux of 1.0 × 1018 ions/m2s, the samples were transferred into the vacuum chamber of the TDS apparatus. After they the samples were transferred into the vacuum chamber of the TDS apparatus. After they


assumed to be 40 eV. After irradiation at room temperature at a flux of 1.0 × 1018 ions/m2s,

were evacuated, the specimens were held at room temperature for a period of time (less

**Figure 1.** The triple ion beam facilities at RIAM Kyushu University: (**a**) tandem-type accelerator attached with two ion guns: terminal voltage 1.0 MeV and (**b**) specimen holder for ion irradiation. **Figure 1.** The triple ion beam facilities at RIAM Kyushu University: (**a**) tandem-type accelerator attached with two ion guns: terminal voltage 1.0 MeV and (**b**) specimen holder for ion irradiation. **Figure 1.** The triple ion beam facilities at RIAM Kyushu University: (**a**) tandem-type accelerator attached with two ion guns: terminal voltage 1.0 MeV and (**b**) specimen holder for ion irradiation.

**Figure 2.** The depth profile of the damage rate (**a**) and the concentration of D<sup>+</sup> at 3.0 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> (**b**) in the case of each accelerating voltage.

accelerating voltage.

Figure 3 shows the damage distribution of the 3.2 MeV Ni3+ ions and the impurity concentration (Ni3+ ions) in the pure Zr following irradiation. The damage estimation was also obtained by the SRIM calculation. The samples for microscopy were thinned by the electropolishing method in which the electrolyte was a mixture of 50 mL perchloric acid and 950 mL acetic acid. During the thinning process, the electrolyte was held at −40 ◦C and the potential applied was 25 V. **Zircaloy-2** 1.38 0.15 0.09 0.05 46 Bal. Figure 3 shows the damage distribution of the 3.2 MeV Ni3+ ions and the impurity concentration (Ni3+ ions) in the pure Zr following irradiation. The damage estimation was also obtained by the SRIM calculation. The samples for microscopy were thinned by the electropolishing method in which the electrolyte was a mixture of 50 mL perchloric acid and 950 mL acetic acid. During the thinning process, the electrolyte was held at −40 °C and the potential applied was 25 V.

**(wtppm) Zr** 

**Sn Fe Cr Ni <sup>H</sup>**

*Quantum Beam Sci.* **2021**, *5*, x FOR PEER REVIEW 3 of 10

**Figure 2.** The depth profile of the damage rate (**a**) and the concentration of D+ at 3.0 × 1021 ions/m2 (**b**) in the case of each

**Table 1.** Chemical composition of the materials used in the present study (wt%).

**Figure 3.** The SRIM calculation [18,19] of the damage distribution and the concentration of Ni3+ atoms in Zr irradiated by Ni3+ ions at 3.2 MeV. The values are estimated in the case of 6.7 × 1014 ions/m2s. **Figure 3.** The SRIM calculation [18,19] of the damage distribution and the concentration of Ni3+ atoms in Zr irradiated by Ni3+ ions at 3.2 MeV. The values are estimated in the case of 6.7 <sup>×</sup> <sup>10</sup><sup>14</sup> ions/m<sup>2</sup> s.

The microstructure was observed before and after irradiation via C-TEM and using a spherical aberration (Cs)-corrected high-resolution analytical electron microscope (JEOL ARM200FC) operated at a voltage of 200 kV in a radiation-controlled area at Kyushu Uni-The microstructure was observed before and after irradiation via C-TEM and using a spherical aberration (Cs)-corrected high-resolution analytical electron microscope (JEOL ARM200FC) operated at a voltage of 200 kV in a radiation-controlled area at Kyushu University.
