A process heat exchanger (PHE) is a key component for transferring the high-temperature heat generated from a very high-temperature reactor (VHTR) to a chemical reaction for the massive production of hydrogen. The Korea Atomic Energy Research Institute has designed and assembled a small-scale nitrogen gas loop for a performance test on VHTR components and has manufactured a small-scale PHE prototype made of Hastelloy-X alloy. A performance test on the PHE prototype is underway in the gas loop, where different kinds of pipelines connecting to the PHE prototype are tested for reducing the thermal stress under the expansion of the PHE prototype. In this study, to evaluate the high-temperature structural integrity of the PHE prototype under the test condition of the gas loop, a realistic and effective boundary condition imposing the stiffness of the pipelines connected to the PHE prototype was suggested. An equivalent spring stiffness to reduce the thermal stress under the expansion of the PHE prototype was computed from the bending deformation and expansion of the pipelines connected to the PHE. A structural analysis on the PHE prototype was also carried out by imposing the suggested boundary condition. As a result of the analysis, the structural integrity of the PHE prototype seems to be maintained under the test condition of the gas loop. 1. Introduction Hydrogen is considered a promising future energy solution because it is clean, abundant, and storable and has a high-energy density. One of the major challenges in establishing a hydrogen economy is how to produce massive quantities of hydrogen in a clean, safe, and economical way. Among the various hydrogen production methods, nuclear hydrogen production is gathering attention worldwide since it can produce hydrogen without environmental burden. Research demonstrating the massive production of hydrogen using a very high-temperature reactor (VHTR) designed for operation at up to 950°C has been actively carried out worldwide, including in the USA, Japan, France, and the Republic of Korea (ROK) [1, 2]. The nuclear hydrogen program in the ROK is strongly considering producing hydrogen by employing a Sulfur-Iodine (SI) water-splitting hydrogen production process. An intermediate loop that transports the high heat generated from a nuclear reactor to the hydrogen production process is needed for the nuclear hydrogen program shown in Figure 1. As a component in the intermediate loop, process heat exchanger (PHE) is a kind of heat exchanger that utilizes the high heat from the nuclear reactor to produce
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