Effects of Long-Term Tritium Exposure on FKM, FFKM, and Epoxy Resin

Historically, the use of polymers in tritium facilities has been limited due to tritium reacting with and degrading organic materials. However, utilizing polymers in a tritium environment would drastically reduce the cost and improve the flexibility of fusion systems through an increased variety of engineering designs. Fluoroelastomers [FKMs (fluorine kautschuk materials)] and FFKMs (perfluoroelastomers), such as commercially available Viton and Kalrez, respectively, have previously been reported to be resistant to tritium interactions. This is a surprising result in the framework of the modern understanding of polymer stability in radioactive environments, which suggests that fluorinated polymers generally perform poorly in any radiation environment.In this study, the stability of both Viton and Kalrez in a pure tritium environment was evaluated. Additionally, Torr Seal, a bisphenol A–based thermosetting epoxy, was tested to determine if the sealant could resist tritium incorporation, as the sealant similarly would be beneficial for vacuum lines and other engineering controls within tritium systems. Viton suffered significant degradation from tritium exposure, becoming more brittle, incorporating significant amounts of tritium, and generating volatile compounds. Kalrez suffered extreme degradation from tritium exposure, turning into a viscous gel, incorporating tritium rapidly, and generating large volumes of volatile compounds.In contrast, Torr Seal suffered minor degradation from tritium exposure, discoloring and becoming somewhat less rigid while incorporating tritium, but did not suffer the same degree of chemical damage nor did it generate significant volatile species. These results suggest that while Viton and Kalrez are unsuited for tritium service, Torr Seal may be suitable for some low-concentration tritium applications.