Hydrogen Isotope Dissolution and Release Behavior of Rare Earth Oxides

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.