Integrated internal-external thermal modeling for packed pebble beds

Abstract

In this study, an integrated external-internal thermal DEM model is introduced in a GPU environment. The external model considers contact conduction and radiation, exhibiting accuracy validated against effective thermal conductivity (ETC) under packed bed conditions. The effective radiation range for a mono-sized packed bed is determined to be 3.5rp, providing accurate predictions of ETC. The internal model integrates FDM-based discretization to solve heat generation, heat conduction and thermal expansion. The model well predicts the temperature gradient of a sphere with partial heat generation. Additionally, preliminary analysis is conducted on the postulated heat generation of packed beds under a complete coolant-loss condition. The results reveal that fission-induced expansion may impact local porosity variations exceeding 2.5%. It is also observed that internally homogeneous models may overestimate heat transfer in packed beds, critical for safety. The model's accuracy and feasibility are demonstrated, providing insights for future research.