Comprehensive investigation of the semi-resolved and resolved LSMPS-DEM for two-dimensional solid particle settling behavior

In the late stages of severe accidents in sodium-cooled fast reactors, molten fuel falls into the liquid sodium coolant, forming a debris bed. The coolability of this debris bed directly influences whether the molten pool will undergo reheat, thereby threatening the integrity of the pressure vessel lower head, which is critical for safety. The coolability of the debris bed is closely related to its shape and size, which in turn depend on its formation behavior. Therefore, accurately simulating the formation process of the debris bed is of great importance. Due to its Lagrangian characteristics, the particle method demonstrates significant advantages in simulating the settling and accumulation processes of particle fragments in liquids. Existing studies have predominantly focused on the application of resolved models, while research on semi-resolved models remains largely confined to grid-based methods, and their applicability in the particle method has yet to be systematically explored. To address this research gap, this study conducts an in-depth analysis of the applicable ranges of resolved and semi-resolved models within the particle method. The results show that in the particle method, when the ratio of fluid particle spacing to solid particle diameter is less than or equal to 0.5, the resolved model should be used; when the ratio is equal to 1 or 2, the semi-resolved model is more suitable. These findings suggest that using the resolved model for large particles and the semi-resolved model for small-to-medium particles could enable more detailed and accurate simulations of debris bed formation behavior, providing a foundation for future investigations into mixed particle size conditions.