Permeability of Protective Coatings to Tritium

The permeability of four protective coatings to tritium gas and tritiated water was investigated. The coatings, including two epoxies, one vinyl and one urethane, were selected for their suitability in CANDU plant service in Ontario Hydro. Sorption rates of tritium gas into the coatings were considerably larger than for tritiated water, by as much as three to four orders of magnitude. However, as a result of the very large solubility of tritiated water in the coatings, the overall permeability to tritium gas and tritiated water is comparable. Marked differences were also evident among the four coatings, the vinyl exhibiting an abnormally high retention of free water because of a highly porous surface structure. It appears that epoxy coatings having a high pigment-to-binder ratio are most suited for coating concrete in tritium handling facilities.