To provide supportive information to understand the current debris status in Fukushima Daiichi Nuclear Power Plant (NPP) Unit-3 (from hereinafter, Unit-3), the meshless, Lagrangian Moving Particle Semi-implicit (MPS) method has been developed for the evaluation of debris-structure interactions in the pedestal region of Unit-3. The developed MPS method incorporated approaches to enhance numerical accuracy and stability, such as second-order corrective matrix and particle shifting technique, and the calculation cost reduction and efficiency improvement strategies to enable plant-scale simulations. A 1/10 scale numerical model of the pedestal region and structures within of Unit-3 and sensitivity analysis conditions were established for simulation cases. The simulation results showed that the convective vapor cooling from the debris surface in the pedestal region and the debris relocation amount/the time intervals between the relocations play important roles in the structure damage due to thermal attacks from the debris.
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