Experimental assessment of palladium-silver membrane for isotope separation, rebalancing and protium removal

The isotope separation, isotope rebalancing, and protium removal are critical functionalities for the fuel cycle of a fusion machine. Nowadays, cryogenic distillation and thermal cycling temperature swing absorption are considered the reference technologies for these tasks, but they are both characterized by high tritium inventory. In the past, the palladium-silver membranes were considered as an option with reduced inventory although some challenges were identified, mainly related to the efficiency of the separation process. This work aims at experimentally investigate the capabilities of this technology for the above-mentioned functionalities in the improved HyFraMe facility at ENEA Frascati laboratories. To do this, the Pd-Ag membrane is preliminary characterized with pure protium and pure deuterium and the permeability and the breakthrough curves are obtained for both the isotopes. After that, the isotope separation tests are performed with different protium-deuterium mixtures. The isotope separation remains a challenging task for the palladium-silver membrane, mainly due to the low efficiency of the process. On the contrary, looking at the isotope rebalancing and protium removal functions, the results obtained in the present campaign are in line with the requirements of a typical fusion machine. Both the functions can be fulfilled with a single and compact permeator which allow to reduce tritium inventory, encumbrances and energy consumption.