Study of Electrolyzer Materials at High Tritium Concentrations

Electrolysis cells are required to drive the combined electrolysis and catalytic exchange process used in heavy water upgrading and water detritiation.

Past projects have used very robust alkaline electrolyte technology for the electrolysis cells, though recently there has been a move toward proton exchange membrane (PEM) technology. In PEM electrolysis a solid polymer electrolyte (SPE) acts as the proton conductor, separator of product gases, and insulator between electrodes.

The long-term effects of highly tritiated water on these SPE materials are not fully understood. At Canadian Nuclear Laboratories (CNL), an exposure study has been undertaken wherein various commercial and proprietary SPE materials were exposed to very highly tritiated water (~1000 Ci/kg, 37 TBq/kg). Exposures were done at a typical cell operating temperature (60°C) for periods that might be expected for commercial operations.

Following exposure, some samples lost sufficient integrity that they could not undergo post-exposure testing. In order to test the remaining materials’ electrolytic performance and physical properties in a nonactive laboratory, a process of decontamination that would result in no further membrane degradation needed to be developed. The successful reduction in tritium content of the samples following decontamination was verified using chemical digestion and combustion analysis. All types of commercial membranes were found to lose significant ion exchange capacity, to show reduced water absorption, and to show reduced strain before failure. Tensile testing showed almost complete degradation even at low doses. In this paper, commercial membrane data are compared with data from CNL’s tritium-compatible membranes.