Numerical investigation on design optimization of core catcher in sodium cooled fast breeder reactor

Core catcher is a passive prevention device that is designed to prevent damage to the lower head of the reactor vessel caused by direct contact with molten corium. In sodium cooled fast breeder reactors (SCFBRs), the structural design of the core catcher directly affects the shape of the debris bed, which in turn impacts the re-criticality and long-term decay heat removal of the debris bed. In this study, the improved discrete element method (DEM) was used to simulate the formation process of the debris bed below the core catcher, and the influencing mechanism of the structure of the core catcher on the shape of the debris bed was explored. Through numerical simulation, the influence on the shape of the debris bed from the projection area of chimney cap, the inclination angle of chimney cap, and the distance between central chimney and surrounding chimneys of the core catcher was examined. It was found that secondary scattering played a significantly positive role in enhancing the uniformity of the debris bed. This study lays a foundation for analysis of the heat transfer performance and evaluation of long-term decay heat removal of debris bed, and can offer engineering guidance for the design and optimization of sodium cooled fast reactor core catcher.