Modelling of Tritium Release from Irradiated Li₂ZrO₃

In this paper we propose a model to explain tritium release from irradiated Li₂ZrO₃ sample made by Mitsubishi Atomic Power Industries Inc. (MAPI). The release curves were obtained by temperature programmed desorption (TPD) techniques in a series of experiments in Kyoto University Reactor (KUR) and in the JRR-4 reactor of the Japan Atomic Energy Research Institute (JAERI). In the model a number of mass transfer steps were taken into account. There were diffusion of tritium in the grain, adsorption and desorption of water on the surface of grains, two types of isotope exchange reactions, water formation reaction in addition of hydrogen to the purge gas. Tritium release curves for different purge gas compositions (N₂, N₂ + H₂O) were calculated to compare with data obtained in the experiments. Apparent diffusivities of tritium in crystal grain of Li₂ZrO₃ were determined.