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 pin bundle configuration in which the molten salt coolant flows parallel to an array of fuel and non-fuel pins.
To aid the further development of FHR designs that employ a pin bundle design, the proposed work addresses the need to develop a full-core thermal hydraulic computational tool that provides detailed temperature, pressure, and flow profiles across the entire core, while incurring a modest computational cost. A steady-state thermal hydraulic model is developed for the solid and annular fuel pin configurations based on the conventional subchannel methodology. The impact of pin power distribution and coolant flow rate on the thermal hydraulic performance of the core is investigated. The results from the subchannel-based model are verified against a CFD model. A transient subchannel model will be developed to investigate the core performance during off-normal scenarios that include both forced and natural circulation cooling. Code-to-code verification with a CFD model will be also performed for the transient model. This model will be used to simulate some of the postulated accident scenarios for this FHR configuration. Insights from these simulations can guide the optimization of core design, and analysis of core safety during accident scenarios.