Hydrogen Isotope Dissolution and Release Behavior of Rare Earth Oxides

Abstract

Hydrogen release behavior from rare earth oxides (REOs) (Y₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃, Er₂O₃, and Yb₂O₃) exposed to 133 Pa of deuterium (D₂) gas or 2 kPa of heavy water (D₂O) vapor at 873 K for 5 h was examined using thermal desorption spectroscopy. Hydrogen solubility and diffusivity in Y₂O₃, Gd₂O₃, Dy₂O₃, Er₂O₃, and Yb₂O₃ exposed to a deuterium-tritium gas mixture (5% to 7% T, 133 Pa) at 873 K and 973 K for 5 h were determined using a tritium imaging plate method. The structural and morphological properties of sintered disk specimens of those REOs were evaluated using an X-ray diffractometer and a scanning electron microscope. From the obtained results, the REO materials were clearly categorized into two kinds in terms of their crystal structure and hydrogen solubility: Monoclinic specimens of Sm₂O₃, Eu₂O₃, and Gd₂O₃ had relatively high hydrogen solubility and diffusivity, while cubic Y₂O₃, Dy₂O₃, Er₂O₃, and Yb₂O₃ had lower ones. The present study suggests that the cubic REOs could be suitable in a nuclear fusion reactor as the tritium barrier materials.

Keywords:

• Rare-earth oxide
• D₂ and D₂O exposure
• tritium exposure
• TIP and TDS methods
• hydrogen dissolution and diffusion

Acknowledgments

This work was partly supported by Joint Research Program of the Hydrogen Isotope Research Center, Organization for Promotion of Research, University of Toyama (HRC2016-09, 2017-04, and 2018-06) and by the Collaborative Research Program of Research Institute for Applied Mechanics, Kyushu University. The authors are grateful to the Hydrogen Isotope Research Center, University of Toyama and Central Institute of Radioisotope Science and Safety, Kyushu University for the support to carry out the tritium experiments.