PURIFICATION OF D2 AND DT GAS BY CRYOSORPTION ON A 5-A MOLECULAR-SIEVE

A DT gas purification process has been developed at the Bruyeres-le-Ch atel Research Center of the French Atomic Energy Commission. This proc ess is based upon the impurities cryosorption on a 5A molecular sieve cooled at 77 K. In order to understand and foresee the cold trap behav iour, adsorption isotherms of several impurities and of hydrogen isoto pes have been determined and modeled. At the same time, several purifi cations of D2 and DT gas streams have been performed at low gas flowra te (5 1 NTP/min). Indeed larger flowrates involve important thermal gr adients and reduce the retention time of the impurities. With this con dition, we have shown that the retention time of an impurity is invers ely proportional to its content in the DT gas stream. For a fixed cont ent 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 in side the cold trap is minimized when saturating the sieve with the imp urities. The major part of tritium is then easily recovered by a singl e expansion of the trap. The experiments prove not only the feasibilit y of the purification of DT gas streams but also the good efficiency o f the process elaborated in our laboratory.