Tritium Migration Process on the Surface and near Defects Studied by In-situ Observation and Ab-Initio Calculation

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Hydrogen isotope behavior in blanket breeding materials and on an oxidized surface of piping materials was studied with focusing on interactions with defects or energetic particles, thorough comparison of results by quantum chemical calculation and experiments (infrared absorption spectroscopy, photoelectron spectroscopy, thermal desorption spectroscopy, and time-of-flight technique).On the oxidized surface of metals, desorption of adsorbed-species was observed by irradiation of energetic particles. The desorption yield and the chemical form of desorbed-species reflected a correlation of surface electronic structures and an incident energy. When the incident energy can induce a fine overlap of the valence band and the conducting band, the desorption yield was meaningfully heightened, corresponding to the electron stimulated desorption.In the bulk of Li_2O, it appeared that hydrogen isotopes is stabilized through trapping by F centers. The energy necessary for detrapping was influenced by the charged state of F centers, and F^0 held the higher trapping force than F^+ by 2 eV. Regarding an interaction with Li vacancy, increase of the diffusion barrier of hydrogen isotopes was found via formation of -OH oriented to the Li vacancy. Moreover, an additional stabilization was attained by mutual aggregation of the -OH.In terms of nuclear fusion engineering, the information obtained in the present study can provide reliable ways to optimize the efficiency of the tritium decontamination by the irradiation of energetic particles, and to assess the tritium inventory in blanket breeding materials.