Helium cooled Gas Fast Reactors (GFR) are designed for producing energy more efficiently and improving safety features such as a total retention of fission products (Xe, I, Cs). This study deals with the diffusion of xenon in refractory liners dedicated to the retention of fission products produced in GFR fuels. The material (W, Mo, W-Re, Mo-Re) will be located in the heart of the nuclear fuel element, where the operating temperature is in the 1000°C- 1600°C range. For the investigation of thermally activated rare gas behaviour, a γ-spectrometry analysis experiment has been performed on the 133Xenon implanted refractory liner. Preliminary results on the 133Xenon release at 1600°C from a tungsten single crystal is presented. In spite of the low concentration of implanted gas (~ppm) and simple microstructure, the prevailing mechanism appears to be complex. One and two dimensional diffusion models are used to characterize or discriminate the highlighted phenomena: burst release, diffusion and trapping of rare gas atoms.