Perfluorinated materials in tritium service

Various perfluorinated materials are used at the Princeton Plasma Physics Laboratory in support of the Deuterium-Tritium experimental program on the Tokamak Fusion Test Reactor (TFTR). For example, SF6 is used as a high dielectric gaseous insulator in the Neutral Beam sources, and Krytox, a perfluorinated polyether, is used as a lubricant in vacuum pumping systems. Each of these materials is robust and stable in the applications for which they are designed but may be a source of trouble when used in tritium systems. This paper reports on the observations made and experience gained operating tritium systems under conditions which degrade these perfluorinated materials. The possible degradation mechanisms and products are described, and the effect on the equipment and instrumentation is described. These observations have led to the conclusion that under certain circumstances perfluorinated materials are not suited for tritium service because of the degradation products from tritium decay and/or process conditions. 11 refs., 1 fig., 1 tab