This paper proposes a model to explain tritium release behavior of an irradiated Li4SiO4 sample made by Forschungszentrum Karlsruhe. The release curves were obtained in a series of experiments carried out using out-pile temperature programmed desorption techniques in the Kyoto University Reactor (KUR). Tritium release curves obtained for different purge gas compositions (N2, N2 + H2, N2 + H2O) were compared for selection of suitable conditions to determine the apparent diffusivity of tritium in a crystal grain of Li4SiO4.

In the model formation, some mass transfer steps in the bulk of the crystal grain and those on the surface of the grain were taken into account, which were diffusion of tritium in the grain, adsorption and desorption of water on the surface of the grain, two types of isotope exchange reactions, and water formation reaction by the addition of hydrogen to the purge gas.

Diffusivities of tritium in the crystal grain of Li4SiO4 were estimated using a curve-fitting method applied to the release curve obtained when the irradiated sample was purged by nitrogen with water vapor because of the fastest tritium release rate observed.