Numerical study on material behavior and core temperature field evolution under CDAs in LFR

Preventing radioactive leakage following a Core Disruptive Accident (CDA) is crucial for protecting the environment and human health. To mitigate such consequences, understanding in-reactor behavior is essential. In this study, a two-dimensional, three-velocity-field and multicomponent simulation code, ACENA, developed at XJTU, is employed to analyze CDA scenarios in the STAR-LM design. Steady-state results are first validated against design parameters to ensure model accuracy, and a hypothetical transient is then introduced to trigger CDA onset. The coupling between damaged core materials and coolant thermal–hydraulic fields is investigated, with particular focus on the motion and distribution of fuel particles with different densities. Results show that low-density fuel particles do not float to the coolant surface but accumulate at the interface between high- and low-temperature regions due to temperature-dependent coolant density variations. Various accident scenarios are further examined to assess material behavior and potential threats to reactor integrity. It is found that local Fuel Blockage Accidents (FBA) cause limited core degradation owing to structural confinement and sufficient cooling when the Primary Heat Exchanger (PHX) remains active, though transient boiling may occur. The study demonstrates ACENA's capability for detailed CDA analysis in Liquid Metal Fast Reactors (LMFRs).