**1. Introduction**

Hydrogen embrittlement of Zircaloy-2 is one of the main factors that limits the life of fuel rods in light water reactor (LWR) fuel-cladding tubes. Because the hydrogen centration exceeds the solid solubility of the metal, some hydrogen atoms are precipitated as hydride, causing hydride embrittlement. To understand how hydrogen pickup during operation influences the growth acceleration of the fuel rod, the effect of hydrogen on the neutron irradiation-induced microstructure should be studied. Hydrogen diffusivity under neuron irradiation is generally controlled by the trapping and de-trapping processes of hydrogen on the material. A dislocation loop is a radiation-induced defect cluster formed by the irradiation of neutrons [1,2], electrons [3,4], or charged particles [5–10]. Second-phase particles (SPPs) also form in Zircaloy-2 [11]. The size distribution of the SPPs and the chemical composition of the cladding tube affect the tube's corrosion rate inside boiling water reactors (BWRs) [12–17]. However, these SPPs are unstable during neutron irradiation and undergo an amorphous transformation resulting in the decomposition and redistribution of the constituent elements the precipitates into defect sinks [15–17]. Ion irradiation has been used on nuclear materials in multiple studies because, unlike neutron irradiation, the displacement per atom (dpa) level, irradiation temperature, and other irradiation conditions can be precisely controlled [5–10].

In this study, 3.2 MeV Ni3+ ion irradiation is applied to Zircaloy-2 samples. The samples are injected with 5.0–30 keV D<sup>2</sup> + ions to understand the trapping and de-trapping

**Citation:** Watanabe, H.; Saita, Y.; Takahashi, K.; Yasunaga, K. Desorption of Implanted Deuterium in Heavy Ion-Irradiated Zry-2. *Quantum Beam Sci.* **2021**, *5*, 9. https://doi.org/10.3390/qubs5020009

Academic Editor: Akihiro Iwase

Received: 22 March 2021 Accepted: 23 April 2021 Published: 26 April 2021

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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.
