[en] Within the framework of a European Community programme aiming at the development of a water-cooled lithium-lead (Pb17Li) blanket concept for a demonstration fusion reactor, important experimental works are devoted to the development of efficient tritium permeation barriers. Among them, in-pile tests (LIBRETTO experiments) with closed capsules containing stagnant Pb17Li are intended to assess under irradiation the efficiency of these barriers. In this paper, a method for interpreting LIBRETTO data is presented, which relies on the use of a 2-dimensional finite element simulation model exploiting the analogy between tritium migration and heat conduction. Preliminary results obtained with this model are also discussed, which seem to indicate that, under conditions comparable with the experiment, the permeation barrier tested in LIBRETTO-2 would reduce tritium permeation by a factor of about 80