Numerical modeling of floating bodies transport for flooding analysis in nuclear reactor building

Highlights: • A coupled scheme for 3D floating bodies transport is developed based on DEM and EMPS. • Verification and validation are carried out through sufficient and systematic tests. • An internal flooding accident with large floating bodies in AP1000 is performed. - Abstract: The nuclear reactor safety analysis especially related to flooding accidents becomes more and more important after the Fukushima nuclear accident. In case of an internal or external flooding accident, some large floating bodies, such as broken doors, emergency powers or even parked vehicles, could cause severe damage and serious problems, requiring the transport studies of moving solids during flooding accidents. The Explicit Moving Particle Simulation (EMPS) method is one of the particle methods, in which large deformation of free surfaces and Lagrangian interfaces can be easily tracked and simulated. Due to its high computational efficiency and easy applicability of the large scale and massively parallel computing, the EMPS method is employed to reproduce the transport of rigid body in free surface flows in this study. The solid-fluid interaction is based on the Passively Moving Solid (PMS) model, while the solid-solid interactions are represented by the discrete element method (DEM). A coupled algorithm, applying different time steps for EMPS and DEM, is proposed in this study. In order to validate this method, several numerical tests are carried out. A wooden block rising from a water tank is simulated to validate the PMS model while the cylinders collapse is calculated to test DEM. Then the freely falling solid body movements with different damping coefficients are simulated to verify the coupled algorithm. Afterward, a 3D dam break flow involving fixed obstacles and a transportable floating body is studied. The histories of water depths and floating bodies' movements are compared with experimental observations. Additionally, another complex 3D dam break event involving multiple floating bodies is simulated for further validation. The trajectories of bodies are investigated, and sensitivity study of the damping coefficient is preliminarily conducted. Finally, in order to demonstrate the capability of the present method, an internal flooding accident with floating bodies transport in AP1000 is presented as an example.