Numerical study of hydrodynamic melt jet fragmentation in sodium-cooled fast reactors based on the improved MPS method

During a core-disruptive accident in a sodium-cooled fast reactor (SFR), as the fuel rods fail, the molten metal fuel may enter the coolant channels in the form of a jet. The fragmentation characteristics of the melt jet are vital for assessing both the resetting behavior of the molten core and the heat removal capacity of the debris bed. This study investigates key factors influencing the hydrodynamic fragmentation of molten jets within SFR cores, focusing on breakup morphology, penetration depth, and fragmentation mechanisms. To achieve this, an improved Moving Particle Semi-Implicit (MPS) method was employed, offering enhanced computational accuracy and stability for simulating molten jet fragmentation under various conditions. The method’s reliability and applicability were validated through comparisons of simulation results with experimental data. The findings revealed distinct fragmentation patterns in sodium coolant, governed by the jet’s velocity and diameter. Specifically, breakup length and time were shown to increase with jet diameter, while velocity exhibited minimal correlation. Based on these insights, a new empirical model was developed to predict jet breakup length in sodium coolant. The correlation was further validated against experimental and other model results, achieving an error margin within ±30%. This research significantly advances the understanding of molten jet dynamics in SFRs, providing a more precise framework for safety evaluations during accidents. Additionally, the numerical simulations elucidate the physical mechanisms underlying jet fragmentation, offering valuable guidance for future reactor designs and safety strategies.