[en] The Japan Atomic Energy Agency (JAEA) has been conducting R and D on hydrogen production by the thermochemical Iodine-Sulfur (IS) process to meet the massive hydrogen demand in the future hydrogen economy. In the IS process, sulfuric acid (H₂SO₄) is evaporated and decomposed into H₂O and SO₃ in a H₂SO₄ decomposer operated under high-temperature condition up to 500degC. We have proposed a new decomposer concept of a block-type heat exchanger made of SiC ceramic, which has a salient corrosion-resistant performance under severe corrosion condition. To verify the mechanical feasibility of the concept, the temperature distributions of sulfuric acid and helium gas were analyzed using a newly coded analytical system applicable to binary mixtures such as H₂SO₄ whose boiling point depends on the concentration. Thermomechanical simulations with a general-purpose FEM code, which used the heat exchange simulation results, showed that the maximum stress was generated around the dryout region, which was about half of the allowable tensile stress of SiC. (author)