Stability analysis of nuclear-coupled thermal hydraulics for a natural circulation lead-cooled fast reactor

Stability analyses of nuclear-coupled thermal hydraulics are carried out for SUPERSTAR – a natural circulation heavy metal (lead-cooled) fast reactor. Attributed to its natural circulation characteristic, flow stability as well as nuclear-coupled thermal hydraulics stability are of some concern. Modal expansion method as an extension for point reactor kinetics is used for neutronics and reduced order model for thermal hydraulic part. These two separate models are coupled through feedback effects. Different scenarios initiated by reactivity and thermal hydraulics conditions are simulated using the coupled models in time domain. It is shown that SUPERSTAR design has considerable stability margin at the nominal operating point. Design becomes less stable as transit time between core exit and core inlet is increased.