Cryocondensation pumping of tritium and its mixtures with D2 and H2

An apparatus used to obtain data on the cryocondensation pumping of deuterium, hydrogen and helium mixtures was modified and moved to a sealed enclosure in the Hot Lab to measure pumping characteristics of tritium on smooth surfaces at 4.2 K. Two cylinders containing approximately 1500 curie of tritium each were used in two experimental runs. Due to a large 3He content palladium thimbles had to be used for purification. At the end of each experiment, T2 was stored in Ti films, evaporated from Ti filament. The pumping speed of T2 was found to be insensitive to the flux and the thickness of the condensed layers behaving much like H2 and D2. The limit on the flux, surface coverage and the cryogen consumption was always imposed by the low 3He trapping efficiency of hydrogen isotopes. T2 vapor pressure at 4.2 K was below our detection sensitivity of 4 x 10-11 Torr. The effects of 18 keV electrons on liquid helium consumption as well as on desorption from composite frozen layer was found to be negligible. THO formed on the walls of our experimental setup by reaction of T2 with H2O present on the surface. This suggests the necessity of a bakeout for equipment which will be used in fusion reactor systems. Finally, total heat contents and thermodynamical equilibrium constants obtained in these experiments were compared with calculations