Hydrogen selective based palladium membranes are important for technological processes such as separation and purification. In general, a Pd-membrane when hydrogenated becomes brittle after certain cycles of α  β hydride transformation due to the accompanied lattice expansion. In order to avoid the embrittlement, alloying of Pd with Ag is generally made. Differently, in Pd-Ag alloys, the lattice has already been expanded by the silver atoms, and the Pd-Ag lattice is less influenced by hydrogen uploading and then less brittle than the pure Pd lattice. We propose to analyze the deuterium filled Pd0.79-Ag0.21 alloy through neutron diffraction using the D1B (High resolution neutron two-axis powder diffractometer) beam line at ILL at constant pressure (100 kPa) and different temperatures, in the range T=100-160°C. This is the temperature region in which the electric resistivity of the alloy passes through the minimum and then it is the region in which it is likely to expect the interstitial tetrahedral sites of the FCC lattice should start to be filled up with deuterium.