THE INFLUENCE OF SURFACE PHENOMENA ON INSITU TRITIUM RELEASE FROM LITHIUM-OXIDE

In-situ tritium release from the single crystals and the sintered pellets of lithium oxide were compared under various hydrogen contents of the sweep gases at 450-820-degrees-C. A model indicating the relative contribution of diffusion in the bulk and the surface rate constant at the solid-gas interface was adopted to analyze the tritium release data. From this analysis, in-situ tritium release of the single crystal was controlled by tritium diffusion in the bulk and its diffusion coefficient was given by D = 2.0 x 10(-3) exp((-81.7 kJ/mol)/RT). The agreement of the diffusion coefficient between in-situ and post-irradiation experiments was satisfactory. Tritium release from the sintered pellet was controlled by the surface rate constant because residence time of tritium in the bulk is very short for a small diffusion path length. It is ambiguous whether to use the grain size or the sample size as a diffusion path length in the sintered pellet.