Thermochemical water splitting by means of the iodine-sulfur (IS) process is one of the promising candidates of CO2-free hydrogen production. Japan Atomic Energy Agency (JAEA) has been conducting R&D on the IS process since the end of the 1980s. A test facility has been constructed using corrosion-resistant industrial structural materials to verify the integrity of chemical plant components and demonstrate continuous and stable hydrogen production. A trial operation was successfully carried out for 8 h with a hydrogen production rate of approximately 10 NL/h. To improve the facility for enhancing the operation stability, a shaft seal technology was developed for a corrosion-resistant pump, which is the key device for feeding HI solution with high concentrations of iodine. The shaft seal technology features purge gas supply and solvent supply to the shaft seal part of the pump to prevent I-2 precipitation, which causes pump malfunction. Upon introduction of the developed shaft seal technology, the duration of the hydrogen production operation was extended to 31 h (hydrogen production rate of approximately 20 NL/h). (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.