Development of a Coupling Process Heat Exchanger Between a VHTR and a Sulfur-Iodine Hydrogen Production System

A heat exchanger to transfer the heat generated from a nuclear reactor to a sulfur-iodine hydrogen production system has been developed. This heat exchanger operates in the extreme environments of a high corrosion, a high temperature, and a high differential pressure. A coating and ion beam mixing surface modification technology are applied to the process heat exchanger in order to enhance its corrosion resistance without loosing the manufacturability of the metal. A Ni-based super alloy is coated with a silicon carbide to enhance its corrosion resistance. The development of heat exchanger including shape design, thermal sizing, ion beam mixing process, stress analysis, and the manufacturing of small scale mock-up heat exchanger are discussed in this paper. The heat exchanger is a hybrid type to meet the design pressure requirements between a nuclear system and a hydrogen production system. A thermal sizing procedure for the process heat exchanger by considering the heat of sulfuric acid gas decomposition is developed. A finite element stress analysis is carried out by using the temperature profile obtained from the thermal sizing calculation. The finite element models were studied to simulate the stress state of the heat exchanger. Two-dimensional analysis was performed at the entrance region of the heat exchanger. A three-dimensional analysis for a single effective heat transfer channel was performed to investigate three-dimensional stress state. Stress analysis results have shown that the developed heat exchanger can withstand the required pressure difference at the elevated temperature condition. A small size heat exchanger was fabricated in order to test it in a high temperature nitrogen-gas loop. The fabrication of the heat exchanger includes a machining of the flow path, a coating and ion beam mixing, and a diffusion bonding of the heat transfer plate.