The high-temperature gas-cooled reactor is a typical fourth-generation nuclear reactor. It has a high core outlet temperature and great potential for process heat utilization. Thermochemical iodine-sulfur cycle hydrogen production is an essential method of process heat utilization of high-temperature gas-cooled reactors that can achieve large-scale, low-carbon hydrogen production and is consistent with the two-carbon strategic goal of China. Furthermore, the development and utilization of clean energy can effectively alleviate the global energy crisis, and hydrogen energy is considered the most promising source of energy in this century and is receiving continuous attention from the industry. The iodine-sulfur cycle includes three chemical reactions: Bunsen, sulfuric acid decomposition, and hydroiodic acid decomposition. Sulfuric acid decomposition is carried out under high temperature and strong corrosive environment, and involves multiple physical and chemical processes such as flow, heat transfer, phase transition and reaction. Therefore, obtaining the thermal and reaction details of this link is critical for improving the efficiency of the iodine-sulfur cycle. Furthermore, it is crucial to study the thermal and decomposition reaction laws of the fluid in the bayonet sulfuric acid decomposition heat exchanger to improve the decomposition rate of sulfuric acid. In this study, the classical Lee model was improved by analogy to the phase transition mass transfer equation and the component transport equation using the phase transition mass transfer rate constant instead of the chemical reaction rate constant, and a coupled model of the sulfuric acid phase transition and two-step decomposition reaction was established. The whole process of sulfuric acid decomposition was simulated, and the effect of the specific surface area of catalyst particles on the decomposition was analyzed. The results show that the temperature of the catalytic reaction zone inside the bayonet heat exchanger meets the requirements of the sulfuric acid core reaction. The phase transition process is relatively brief, yet it can effectively enhance the direct heat exchange between sulfuric acid and helium. As the sulfuric acid flow increases, the length of the two-phase section also increases. The first decomposition and phase transition of sulfuric acid occur almost simultaneously. The reaction is complete, the conversion rate is high, and the molar fraction of sulfur trioxide is up to 46%. The second-step decomposition of sulfuric acid permeates the entire zone of catalytic activity. The first half zone has a high conversion rate, and the sulfur dioxide molar fraction is up to 33%. Since the gas mixture in the inner tube continuously transfers heat to the sulfuric acid in the annulus, the temperature of the gas mixture at the outlet is lowered, and a small amount of sulfuric acid is produced. The research results also show that when the specific surface area of the catalyst particles is large, the overall rate of sulfuric acid decomposition is significantly improved. The highest rate of sulfuric acid decomposition under the design conditions is about 85%.

The present study proposes a segmented cooling-stream injection structure based on a certain coolant mass flow rate, and numerically investigates the effect of segmented cooling-stream injection on supersonic film cooling. The results indicate that without shock-wave impingement and with helium as the coolant, segmented cooling-stream injection can reduce the mixing between the mainstream and the cooling stream to produce better cooling performance than single injection, especially at larger coolant Mach numbers. However, with nitrogen as the coolant, the cooling effect of the segmented-injection system is very close to that of the single-injection system. Mixing at the impinging region is enhanced significantly when there is an incident shock wave. When the shock wave impinges between the two coolant inlets, segmented cooling-stream injection improves film cooling effectiveness in the midstream and downstream regions more than single injection because only part of the cooling stream undergoes the enhanced mixing effect of the shock wave. The advantage of segmented injection is reduced when the impinging region is behind the second coolant inlet. The further downstream the impinging region, the smaller the associated advantage.

The impact of graphite dust on structural equipment is a potential safety hazard in HTGR. The present study focuses on the graphite particle deposition process on the deflector in the inlet passageway of intermediate heat exchanger and analyzes the effect of particle size on inertial deposition and diffusion deposition. Meanwhile, the particle rebound behavior is considered when the particle impacts the wall. To determine the relevant parameters of the rebound model, the experiments about adhesion are carried out and validated. Then the flow field is simulated in the inlet passageway of intermediate heat exchanger based on k–ε turbulent model, and particle trajectories are predicted by a discrete particle model with rebound boundary. The results show that adhesion force by measures is obviously smaller than theoretical model. In addition, the particle deposition rate decreases first and then increases, and the rebound model makes deposition results more actual.