In thermonuclear fusion reactors, the continuous purification of the plasma exhaust from the impurities present in very low concentrations is required as well as the separation of hydrogen from the DT streams. To obtain this aim, several fixed-bed adsorbers of modified zeolites have been proposed to treat the plasma exhaust stream related to the tritium parameters for the NET Phase II Programme. The adsorption equipment consists of a series of columns containing different types of zeolites characterized by their selective removal of groups of impurities of which those containing tritium are periodically removed by supporting units according to the mass flow sheet proposed and discussed. The final impurity-free hydrogen isotope stream is submitted to gas chromatography for the removal of hydrogen from the other isotopes. Other alternative techniques such as gas chromatography by displacement and pressure swing parametric pumping, are taken into consideration. Major emphasis has been put on the substrates used in the hydrogen isotopic separation system. The characteristics of the most promising zeolite, the (Ca,Na) mordenite small pores (SP), are described. The adsorption isotherms, the kinetics of adsorption for most of the components constituting the plasma exhaust stream are given at different temperatures and pressures, which are indispensable for predicting the performance of the adsorption equipment.