SUMMARY

Fluoride-salt-cooled high-temperature reactors (FHRs) are an emerging category of reactors that combine the graphite-matrix coated-particle fuel developed for high temperature gas reactors (HTGRs) with a high heat capacity, single-phase molten salt coolant. 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, the proposed work addresses the need to improve the understanding of the fluid flow dynamics and heat transfer characteristics for a molten salt coolant. In this study, a test section representing a single coolant channel is developed, and a heat transfer test facility is fabricated to experimentally measure the heat transfer coefficient and frictional pressure gradient of a surrogate fluid which 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 will be developed to predict the heat transfer and pressure drop for such flows experienced in the plate type FHR. Insights from these experiments and analysis can guide the further development of plate type FHRs by improving the confidence levels in the predictions of safety analysis codes, therefore supporting the licensing of these reactors.