Development of semi-empirical model for tritium permeation under non-uniform temperature distribution at heat exchanger tube wall

Prediction and mitigation of tritium permeation is an important safety issue in high temperature gas-cooled reactors (HTGRs) especially for industrial applications such as hydrogen production and process heat. This study investigated the effect of non-uniform temperature distribution on the tritium permeation rate through the heat exchanger wall and improved the prediction capability of the existing models by reflecting it. To be more explicit, the effective diffusivity (Dm) and the effective temperature (Tm) was newly defined for the heat exchanger wall, and the effective weight (xeff) was derived from one-dimensional diffusion equation. Based on the data collected by numerical methods, an empirical correlation for xeff was developed by a linear regression method and it was validated by comparisons with randomly generated separate numerical solutions. As a result, the new permeation model based on the effective temperature (Teff) showed very good agreement with the numerical results within an error of 1.28% on average while the existing model based on the average wall temperature (Tm) showed large discrepancies exceeding 200% in the maximum error. This study concludes that the newly developed tritium permeation model significantly improves the prediction capability on the tritium permeation rate through the heat exchangers. Which is the main tritium transport path in the high temperature reactor and the integrated industrial process systems.