In the framework of next fusion machines, the tritium cycle is of particular interest since its central role in fusion reaction as a fuel element. The high permeability of Tritium, as well as its decay time, requires an “in situ” production. The Tritum Extraction and Removal System is the system aimed to manage the tritium cycle inside the reactor and the Permeator Against Vacuum (PAV) is one of the technologies proposed for the TERS of the Water-Cooled Lithium Lead Breeding Blanket. The aim of this work is to develop a lumped model for the tritium extraction based on the PAV. This work is carried on in collaboration with the research centre of ENEA-Brasimone (Camugnano, BO) where a PAV mock-up has been installed and is under test in the TRIEX-II facility.