Development of a New Thermochemical and Electrolytic Hybrid Hydrogen Production System for Sodium Cooled FBR

Abstract

A new thermo-chemical and electrolytic hybrid hydrogen production system in lower temperature range is newly proposed by the Japan Nuclear Cycle Development Institute (JAEA) to realize the hydrogen production from water by using the heat generation of sodium cooled Fast Breeder Reactor (FBR). The system is based on sulfuric acid (H₂SO₄) synthesis and decomposition process developed earlier (Westinghouse process), and sulfur trioxide (SO₃) decomposition process is facilitated by electrolysis with ionic oxygen conductive solid electrolyte to reduce the operation temperature 200-300°C lower than Westinghouse process. SO₃ decomposition with the voltage lower than 0.5V was confirmed in the temperature range of 500 to 600°C and theoretical thermal efficiency of the system evaluated based on chemical reactions was within the range of 35% to 55% under the influence of H₂SO₄ concentration and heat recovery. Furthermore, hydrogen production experiments to substantiate the whole process were performed. Stable hydrogen and oxygen production were observed in the experiments, and maximum duration of the experiments was about 5 hours.