Study on kinetics of hydrogen dissolution and hydrogen solubility in oxides using imaging plate technique

Using a tritium imaging plate technique, kinetics of tritium dissolution and its solubility in several oxides were examined. Mirror-polished single crystals of alumina, spinel and zirconia were used as specimens, which were exposed to 133 Pa of a tritium(T)-deuterium(D) gas mixture (T/(T + D) ∼ 0.17) at temperatures ranging from 673 to 973 K for 1-5 h. The T surface activity on the specimens increased with increasing temperature and exposure time, it almost saturated at 873 K and reached 2 × 10⁵ Bq/cm² (1 × 10¹⁴ T/cm²), and no clear difference appeared among the types of specimens. The T activity in the oxide bulk also increased with temperature, in which there was a trend for the oxides: spinel ≧ zirconia ≧ alumina. In the T dissolution process for all oxides, the concentration gradient due to its diffusion was not observed even for short exposure times: the T density was almost uniform over the specimens in transition states and increased with exposure time up to the saturated value. These experimental results suggested that the rate-controlling process of T dissolution in the temperature region should be not its diffusion in the oxides but dissociation of hydrogen molecules (T-D mixture in this case) into atoms, its adsorption on the surface and/or T penetration from the surface into the bulk.