Fluid Flow and Heat Transfer Characteristics of High Prandtl Number Fluids for Fluoride-Salt-Cooled Reactor Applications
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Ragoowansi, Evan Ashvin
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Abstract
Fluoride-salt-cooled high-temperature reactors (FHRs) are a new and developing class of reactors that features low-pressure liquid fluoride salt cooling and the graphite-matrix coated-particle fuel developed for high temperature gas reactors (HTGRs) and are designed for a high-temperature power cycle. FHRs have several economic and safety benefits due to higher core power densities compared to HTGRs: near-atmospheric pressure operation, higher safety margins for fuel failure and coolant boiling, and passive decay heat removal using natural circulation. One of the potential fuel designs for FHRs is the plate type configuration in which the molten salt coolant flows in the wide, narrow channels between the array of parallel fuel plates. To aid the further development of FHR designs that employ a plate-type fuel design, this work addresses the need to improve the understanding of the fluid flow dynamics and heat transfer characteristics for a molten salt coolant. The nature of the molten salt requires the flow to be in the transition regime, making predictions based on the literature difficult. In the present study, a test section representing a single coolant channel is designed and fabricated, and a heat transfer test facility is fabricated to measure the heat transfer coefficient and frictional pressure gradient of a surrogate fluid that matches the pertinent dimensionless parameters of molten salt in a plate-type FHR. In addition to the plain coolant channel, a channel with lozenge-shaped dimple features is also developed to study potential heat transfer enhancement. Based on these experimental results, models are developed to predict the heat transfer and pressure drop for such flows experienced in the plate-type FHR. These models are compared with a steady state computational fluid dynamics (CFD) model and a model developed in the thermal-hydraulic program TRACE for a single coolant channel. The experimental study serves as a preliminary verification of the models that use CFD and TRACE. The correlations developed in this study are then used to estimate the temperatures in the core and the overall cooling capacity, demonstrating the benefits of an FHR over conventional reactors. Insights from these experiments and analyses will guide the further development of plate-type FHRs by improving the confidence levels in the predictions of safety analysis codes, thereby assisting the licensing of these reactors.
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2025-05-07
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Dissertation