Experimental Investigation on Helium Drag Effect in Terms of Natural Circulation Enhancement for Passive Molten Salt Fast Reactor (PMFR)

Abstract

A helium bubbling system employed in molten salt reactors for the elimination of insoluble fission products improves a natural circulation performance of working fluid owing to an intensified drag force of helium bubbles. In this regard, to evaluate the extent of natural circulation enhancement, adiabatic two-phase natural circulation experiments were performed. In this experiment, the variation of major thermal-hydraulic parameters such as a velocity of the working fluid and volume fractions of gas-phases was observed according to the modification of sensitivity variables including the width of riser channel, the type and quantity of gas, and the viscosity of working fluid. A complicated bubbles’ behavior was captured through a high-speed visualization within the wide range of gas injection rate from 1 to 15 lpm. Based on the experimental findings, the width of the riser channel showed a major effect on the natural circulation performance. Moreover, helium resulted in a superior enhancement in the circulation compared to air because of a larger density difference with the working fluid. As the viscosity of the working fluid increases, fluid velocity decreased non-linearly. Experimental outcomes showed that the helium bubbling system can elevate the natural circulation performance of working fluid. This study will contribute to investigating the helium bubbling effect with respect to the circulation performance of working fluid in a passive molten salt fast reactor (PMFR).