Natural circulation cooling for lead-bismuth cooled simple reactor

This study investigates the maximum power output that can be removed using natural circulation alone in a small, 150-MWt reactor cooled with lead-bismuth mixture. First, a simple natural circulation model in the core will be analyzed. Then the model will be coupled with the secondary extemal cooling system to make it more realistic. Two possible directions of forced secondary flow were analyzed: a concurrent flow with the primary reactor coolant flow, and a countercurrent flow that would flow against the primary coolant flow. Flow equations were derived from the conservation of momentum equation, which was simplified to the differential pressure loss through the core and the driving differential pressure due to buoyancy forces. A parametric study was conducted on the effect of varying reactor height, secondary coolant velocity, fuel pitch, and fuel height, in order to determine the maximum amount of heat that can be removed from the core. The results show that it is not feasible to cool 150-MW of heat using natural circulation, however the decay heat may be removed for a vessel that is 20 m high