Performance Testing of a Prototype Pd-Ag Diffuser

A prototype Pd-Ag diffuser manufactured by Power and Energy was evaluated for performance characterization testing at the Savannah River National Laboratory (SRNL). The prototype Pd-Ag diffuser was characterized to determine the overall performance as a function of the permeation of hydrogen through the membrane. The tests described in this report consider the effects of feed gas compositions, feed flow rates, pump type and internal tube pressure on the permeation of H₂ through the Pd-Ag tubes.

For the 96% H₂/4% N₂ mixtures, nearly all of the H₂ permeated through the membrane at flow rates up to 3000 sccm. However, results for the 50% H₂/50% N₂ composition show that 100% permeation is only achieved up to a flow rate of 1000 sccm. A significant reduction in the hydrogen permeation was observed for the 2% H₂/98% N₂ composition. This Pd-Ag diffuser design is not suitable for a tritium purification system within the fusion energy fuel cycle. Typical tritium purification systems can be expected to see a range of hydrogen isotope concentrations and this particular prototype diffuser is only suitable for process streams containing high concentrations of hydrogen isotopes.

Significant efforts should be undertaken to identify additional commercial vendors for Pd-Ag diffusers. It is of critical importance to identify, procure, and test different Pd-Ag designs that can perform well over a range of hydrogen isotope concentrations for tritium gas processing applications.