One of the design targets for the ITER Tokamak Exhaust Processing system is to suppress the loss of tritium to less than 10-5 g/h into the Normal Vent Detritiation System of the Tritium Plant. The plasma exhaust gas, therefore, needs to be processed with an overall tritium removal efficiency of about 108. Such a high decontamination factor can be achieved by multistage processes. The third step of the three step CAPER process developed at the TLK is based on a so-called permeator catalyst (PERMCAT) reactor, a direct combination of a Pd/Ag permeation membrane and a catalyst bed. In this work, a numerical simulation of the PERMCAT reactor was performed and the result was compared with experimental data.