Hydrogen Absorption Behavior on Zirconium under γ-Radiolysis of Nitric Acid Solution

Abstract

　Zirconium (Zr) has been used as a structural material at the spent nuclear fuel reprocessing plant in Japan because of its excellent corrosion resistance against nitric acid solution. However, radiolytic hydrogen is known to be generated in spent nuclear fuel solution. Zr is known to be highly susceptible to hydrogen embrittlement. Therefore, evaluating the radiolytic hydrogen absorption behavior of Zr in nitric acid solution (HNO₃) is essential. In this study, immersion tests were conducted on Zr in nitric acid solutions under γ-ray irradiation to evaluate its radiolytic hydrogen absorption behavior. Results showed that the hydrogen concentration on Zr increased in both 1–3 mol/L HNO₃ and pure water upon irradiation of 5 and 7 kGy/h after immersion. The amount of hydrogen absorption on Zr under γ-ray irradiation had a direct correlation with the amount of radiolytic hydrogen generated in HNO₃. The results of glow discharge optical emission spectrometry, thermal desorption spectroscopy, and X-ray diffraction show that the absorbed radiolytic hydrogen generated a hydride on the surface of Zr.