Japan Atomic Energy Agency has been conducting research and development on a thermochemical water-splitting cycle featuring iodine- and sulfur-compounds (called an IS process) as one of promising heat utilization systems of High Temperature Gas-Cooled Reactors. We have prepared polymer electrolyte membranes by the radiation-induced graft polymerization and cross-linking methods and then have investigated their applicability to electro-electrodialysis (EED) for concentrating HI in an HI-I2-H2O mixture. For practical applications, EED membranes are required to be stable in the severe environment of high-temperature strongly acidic solutions. We thus examined thermal, chemical and electrochemical stabilities of the radiation-grafted membranes under the conditions of the actual EED operation over 100 hours, while measuring the time evolution of a cell voltage and a change in the ion exchange capacity between the EED experiment. The results showed that chemical cross-linking in the graft chains could largely improve the membrane stability.

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