Surface and bulk effects:

Surface and bulk effects have been noted in numerous polymer/tritium studies.  Within one study, hardening of neoprene occurred by the bulk, although hardening of natural rubber primarily occurred at the surface (crack propagation). Overall incorporation of tritium into a polyethylene powder was searched not to be a function of the amount of powder, but of the exposed surface area. Radiation-induced fluorescence from the surface of high-density polyethylene exposed to tritium was displays to be sequences of magnitude greater than that from the bulk.

Polyimides (good in the presence of gamma radiation) appear good in tritium handling and are recommended. Vespel stem tips for valves, while used along with enough sealing force, continue to seal for variosu years in tritium (STP).  While used with less sealing force, therefore, leaks have been noted across valve tips, probably since of surface hardening.  The Polyimide gaskets under constant sealing load are possibly adequate for years.

Saturated hydrocarbon mineral oils (for instance, Duo-Seal) need often changes in tritium service since of vapor pressure raise (offgassing) and liquid viscosity raise.  Silicone oils are rapidly polymerized or solidified. It is ether oils last for years in same service, but are expensive and might absorb important amounts of tritium.

Fluorinated pump oils are not optional for tritium service and certainly not for tritiated water vapor service. Tritium fluoride evolution and corrosion might result.