One of the reference technologies for the fuel cycle of fusion machines is Pd/Ag membranes. This technology is proposed to be implemented in tritium recovery systems because of their exclusive selectivity toward molecular hydrogen isotopes (Q = H, D, T). To perform scaling-up studies for the Tritium Extraction and Removal System of the European DEMOnstration fusion power reactor (DEMO) with a solid blanket, a one-dimensional simulation code was recently developed and successfully validated with experiments. This code relies on different operational (e.g., feed pressure and temperature), geometrical (e.g., permeator length), and membrane-intrinsic (e.g., Q2 permeability) parameters given as input. The main outcome is the Q2 permeation efficiency, defined as the Q2 permeate–to–feed flow ratio. Because of the low concentrations of Q2 expected at the He stream purging the solid blanket, the surface effects are expected to be important, decreasing the separation efficiency of the Pd/Ag permeators. In this paper the role of surface effects on the permeation efficiency is studied for a DEMO-relevant scenario (feeding mixture: HT/H2/He). Moreover, a sensitivity study is also given demonstrating the high impact of the permeation area, temperature, and feed pressure on the permeation efficiency of HT.