AbstractA DT gas purification process has been developed at the Bruyères-le-Châtel Research Center of the French Atomic Energy Commission. This process is based upon the impurities cryosorption on a 5A molecular sieve cooled at 77 K. In order to understand and foresee the cold trap behaviour, adsorption isotherms of several impurities and of hydrogen isotopes have been determined and modeled. At the same time, several purifications of D2 and DT gas streams have been performed at low gas flowrate (5 1 NTP/min). Indeed larger flowrates involve important thermal gradients and reduce the retention time of the impurities. With this condition, we have shown that the retention time of an impurity is inversely proportional to its content in the DT gas stream. For a fixed content of a mixture of impurities, the overall retention time is only due to differences between the adsorption capacities of the sieve towards each of these impurities. On the other hand, the tritium inventory inside the cold trap is minimized when saturating the sieve with the impurities. The major part of tritium is then easily recovered by a single expansion of the trap. The experiments prove not only the feasibility of the purification of DT gas streams but also the good efficiency of the process elaborated in our laboratory.