In HCLL (Helium Cooled Lithium Lead) blanket for ITER fusion reactor, an efficient management operation of tritium is necessary, in order to minimize the release of tritium to the environment and to improve the economy of the overall balance of the reactor tritium inventory. In this context, optimization techniques for the measurement of tritium in the various stages of the fuel cycle of the reactor must be carried out in parallel with the research and development of processing systems for tritium. For example, the TES, Tritium Extraction System, is a critical system and the determination of the concentration of hydrogen isotopes is required for its correct design [1]. Therefore, the need of a fast and reliable sensor for the measurement of the tritium concentration in the liquid breeder is well established. For this application, a sensor based on the principle of tritium permeation in a capsule of suitable material seems to be, at least in principle, the easiest and most reliable one. Furthermore, many data on tritium permeability through different materials and their compatibility in an environment of liquid metal are available, thanks to the experimental studies performed for the selection of structural materials for blanket modules.