Diffusion/desorption of tritium from irradiated beryllium

This report discusses stepped-thermal-anneal tritium-release measurements at 573 up to 1173 K which have been performed on irradiated Be test materials, fabricated and irradiated to meet conditions relevant to the International Thermonuclear Experimental Reactor (ITER). A combined diffusion/desorption model for tritium release allows determination of diffusion coefficients and desorption-rate constants in the mixed-mechanism regime where both diffusion and surface desorption appear to be rate-limiting. The effective tritium diffusivities (m2/s) for these materials, and also from new data analysis of previously reported fully dense material, were found to be: 81% TD Be:1.7 x 10-11 exp(-3.5 kJ/mol/RT); 99% TD Be:1.6 x 10-10 exp(-9.5 kJ/mol/RT); 100% TD Be: 1.4 x 10-10 exp(-11.5 kJ/mol/RT). Tritium release data for both the 81% TD and the 99% TD sample were matched reasonably well by the diffusion/desorption model. The model provides evidence for a changing mechanism over both temperature and density, but indicates that diffusion is the primary mechanism with a small and changing contribution from surface desorption