Effect of gas-film resistance on hydrogen permeation flux through Pd membrane

In the fuel cycle of a fusion reactor, palladium diffuser purifies hydrogen isotopes. We have developed the numerical code of hydrogen permeation through palladium alloy membrane in consideration of each elementary reaction step and effect of external gas-film resistance of mass transfer on hydrogen permeation through palladium alloy membrane was quantitatively evaluated using the code. In the absence of external mass transfer resistance, the rate-controlling step of mass transfer through palladium alloy membrane is solid state atomic diffusion in the range of operating temperature and recombinative desorption at low partial pressure side at lower temperature. The temperature for shifting the rate-controlling step from solid state atomic diffusion to recombinative desorption at low partial pressure side becomes higher as the membrane thickness is thinner. The thinner membrane thickness is admittedly preferable for increasing in hydrogen permeation flux. However, the effect of external gas-film resistance of mass transfer on hydrogen permeation flux through palladium alloy membrane should be considered when the membrane thickness is less than 10μm. Especially in case of insufficient hydrogen pressure on high partial pressure side of membrane, hydrogen permeation flux remarkably decreases due to external gas-film resistance. (author)