Comparison of modelling of tritium release from ceramic breeder materials

Out of pile tritium release experiments were conducted using a lithium silicate breeder irradiated in a research reactor. The tritium release curve obtained using a wet sweep gas was analyzed with several models. In the models, the effect of surface reactions were eliminated since the wet purge gas significantly enhances the isotope exchange reactions that take place on the grain surface. First, simple linear driving and diffusion models were tested. However, it was found that these models cannot well reproduce the experimental release curve. Next, trapping and detrapping reactions were incorporated to these models. Then, the improved models successfully reproduced the experimental release curve of tritium. Furthermore, another diffusion model, in which a resistance at sub-surface layer is accounted for, was tested. This model was also found to well reproduce the experimental results. However, the activation energy of diffusivity obtained in this model is considerably smaller than those obtained in other models.