Abstract
Molten Salt Reactors (MSRs), a Generation IV nuclear reactor concept, benefits from molten salt as a coolant. It offers advantages like low operating pressure, and high operating temperature for improved thermodynamic efficiency. Another advantage of many molten salt reactor designs is utilizing natural circulation to provide passive safety by enabling coolant flow without external pumps. As many molten salt reactor systems rely on natural circulation for reactor cooling under accident conditions and, in some cases, normal operating conditions, it is important to have a sound understanding of the fundamentals of natural circulation and demonstrate its performance for relevant operating conditions.To this end, the purpose of this study is three-fold: (1) characterize natural circulation phenomenology by evaluating relevant dimensional (e.g., mass flow rate, driving head, temperature difference) and non-dimensional (e.g., Grashof number, Richardson number, heat source number) parameters as heater power and fluid type vary; (2) establish the thermal hydraulic viability of a natural-circulation-driven molten salt reactor through use of a surrogate fluid (Therminol-66); (3) demonstrate that global performance of a natural circulation system is similar for both surface-heated and volumetrically-heated (Ohmic heated) test loops under similar thermal conditions.
By accounting for flow resistance through a test loop, extensive testing and analysis show that the use of a properly selected surrogate fluid can be used to demonstrate the thermal hydraulic viability of a natural-circulation-driven molten salt reactor. Also, experimental data shows that global performance of a natural circulation system does not appreciably change when method of heat delivery is varied between surface-heated or volumetrically-heated provided that other key thermal conditions are maintained.