SF/sub 6/ and water cold trap for TFTR deuterium-tritium operations

Abstract

The Tokamak Fusion Test Reactor (TFTR) vacuum system is being upgraded to trap SF/sub 6/ gas which may leak from the neutral beam injectors during the planned deuterium-tritium experiments. This is necessary since SF/sub 6/ can, in 25% of a gram-mole, completely inactivate the platinum catalyst in the tritium cleanup system (TCS). Any SF/sub 6/ leaking into the injectors will initially be held on the liquid helium or liquid nitrogen cryopanels. During regens of the liquid helium panel, the deuterium and tritium will pass to the TCS, with the SF/sub 6/ being retained on the cryopanels. In the final phase of the accident recovery scenario, the cryopanels will be warmed to room temperature and the SF/sub 6/ collected by a liquid-nitrogen cooled cold trap. Design of the cold trap and measurements of the vapor pressure of SF/sub 6/ at 77 K as a function of surface coverage are presented. The SF/sub 6/ vapor pressure at 77 K, with only a few monolayers absorbed, was found to be <10/sup -7/ torr. Modest pressures of approximately 10/sup -5/ torr were measured after nearly 3*10/sup 5/ torr-1 were deposited on a cold trap with an area of 0.1 m/sup 2/. In the final configuration, the cold trap will also be used to collect water which may have accidentally leaked into the vacuum system.<>