Analysis of Autonomous Load Following (ALF) in Advanced Fast Reactors

The Autonomous Load Following (ALF) properties of fast-spectrum nuclear reactors offer great potential for increased electric grid stability, reduction in control rod mechanism wear, and less operator action for small power transients. These features can result in design simplification and enhanced safety of reactor systems. Thermal-hydraulic transients result in reactivity feedback from the coolant to curb power transients and return the reactor to a stable, critical condition. The speed of the reactivity feedback and the resulting limit of ALF controllable transient size are based to a great extent on the intrinsic properties of the coolant and their effects on the reactor kinetics. Lead, Lead Bismuth Eutectic (LBE), and Sodium are the coolants with the most promising options for advanced fast reactors under the Generation IV program. This paper reviews the properties of each coolant type and presents the reactor kinetics modeling results of analyses using the TRACE code to simulate their respective reactivity response for a simplified fast reactor design. This provides insight into a comparison of coolant types based on reactivity feedback and autonomous load following capability in future fast reactor designs.