Design and Development of a Tritium-Compatible Electrolyzer

Abstract

Proton exchange membrane (PEM) electrolysis is the process of cracking water into hydrogen and oxygen using a PEM electrolyzer. The PEM electrolyzer consists of a PEM, bipolar plates, insulators and end plates. In this study, a PEM electrolyzer is designed and developed for its application in the nuclear industry for tritium removal using the catalytic exchange electrolysis process. Tyne, in collaboration with CNL, has designed a tritium-compatible PEM electrolyzer with specially designed 20.3 cm active diameter electrodes which can withstand tritium better than ordinary Nafion^® and with enhanced safety features. Electrochemical and hydrodynamic models are used in the design stage to determine various design parameters. A prototype with 1 Nm³ /hr design capacity is built and tested with Nafion^® N-117. The polarization curve is experimentally determined at ambient temperature and pressure. The results showed that the required single cell potential is 3 V at 1.0 A/cm² . As a second phase of the electrolyzer development, tritium-compatible membrane, specifically developed for tritium application at CNL, was soaked in tritiated water for 3 months and then detritiated for several months. The detritiated membrane has been then tested in a smaller unit. Compared to the soaked Nafion^® membranes the specially designed and developed tritium-compatible membranes perform better and thus are to be used in final electrolyzer assembly.