Analysis Model for Sulfur-Iodine and Hybrid Sulfur Thermochemical Cycles

This paper presents a transient control volume modeling scheme for both the sulfur-iodine (SI) and Westinghouse hybrid sulfur (HyS) thermochemical cycles. These cycles are very important candidates for the large-scale production of hydrogen in the 21st century. In this study, transient control volume models of the SI and HyS cycles are presented, along with a methodology for coupling these models to codes that describe the transient behavior of a high-temperature nuclear reactor. The transient SI and HyS cycle models presented here are based on a previous model with a significant improvement, namely, pressure variation capability in the chemical reaction chambers. This pressure variation capability is obtained using the ideal gas law, which is differentiated with respect to time. The HyS model is based on a time-dependent application of the Nernst equation. Investigation of the new pressure assumption yields a peak pressure rate of change of 5.877 kPa/s for a temperature-driven transient test matrix and 2.993 kPa/s for a mass flow rate-driven transient test matrix. These high rates of pressure change suggest that an accurate model of the SI and/or HyS cycle must include some method of accounting for pressure variation. The HyS model suggests that the hydrogen production rate is directly proportional to the SO₂ production rate.