Fusion reactor high vacuum pumping: charcoal cryosorber tritium exposure results

Recent experiments have shown the practicality of using activated carbon (coconut charcoal) at 4 K to pump helium and hydrogen isotopes for a fusion reactor. The long-term effects of tritium on the charcoal/cement system developed by Grumman and LLNL was not known; therefore, a program was undertaken to see what, if any, effect long-term tritium exposure has on the cryosorber. Several charcoal-on-aluminum test samples were subjected to six months exposure of tritium at approximately 77 K. The tritium was scanned several times with a residual gas analyzer and the speed-capacity performance of the samples was measured before, approximately one-third of the way through, and after the exposure. Modest effects were noted which would not seriously restrict the use of charcoal as a cryosorber for fusion reactor high-vacuum pumping applications. Considering that charcoal in a fusion reactor environment will be exposed to higher tritium pressure only during regeneration, it should be possible to design and operate a cryopump system capable of years of operation without tritium degradation effects