Release kinetics of tritium generated in lithium-enriched Li_(2+x)TiO_3 by thermal neutron irradiation

摘要

Tritium release kinetics for Li_(2+x)TiO_3, the lithium-enriched Li_2TiO_3, was investigated by isochronal and isothermal annealing experiments. Tritium release by isochronal annealing showed that the dominant release stage was found at around 600 K. An additional release stage at lower temperature side was appeared with increasing excess lithium, which was attributed to the release of tritium trapped in Li_4TiO_4 structure. The dominant release stage was considered to a release of tritium trapped by irradiation defects. Isothermal annealing experiments indicated that tritium releases were controlled by diffusion process. The diffusion coefficient of Li_(2.0)TiO_3 was one order of magnitude as large as those of Li_(2.2)TiO_3 and Li_(2.4)TiO_3, although their activation energies were almost the same. These results showed that rate-determining step was the diffusion process of tritium in Li_2TiO_3 structure for Li_(2+x)TiO_3 and excess lithium would make diffusion coefficient smaller. Simulation of tritium-TDS spectra for Li_(2.0)TiO_3 has clarified that the TDS spectrum forLi_(2.0)TiO_3 can be demonstrated by using Arrhenius diffusion parameters obtained by isothermal annealing experiment in the present study.