Deuterium Permeation Through a Self-Supported Palladium-Silver Membrane in Helium Gas Mixtures

Palladium membranes and membrane reactors can separate and purify tritium from impurities in the plasma exhaust processing system for the fusion energy fuel cycle. Membranes can also act as a continuous separation method to remove tritium from helium streams in the breeder blanket tritium extraction system, such as from the purge gas of solid breeders. To investigate the potential of these membranes for these applications, we performed a deuterium permeation campaign with a self-supported palladium-silver (Pd-25Ag wt%) tube of 0.15 m length, 76
$\mu$
m wall thickness, and 3.0 mm inner diameter. A gas mixture of 3.95% D
$_{\text{2}}$
and a balance of He was delivered to the inside of the tube and D permeated radially outward through the membrane into a vacuum chamber. Permeation experiments were conducted at 300
$^{\circ}$
C, 350
$^{\circ}$
C, 400
$^{\circ}$
C, and 450
$^{\circ}$
C, from 100 to 1000 sccm total flow rate, and with total pressures of 90, 150, 190, and 250 kPa. Deuterium permeation was consistently lower than predicted from diffusion-limited permeation models, thus we developed a transport model that included gas-phase mass transfer and surface reactions to model experimental results. The dissociation constant was optimized to fit the developed model to experimental data.