Study on Fuel Rod Melting and Molten Material Migration in Core Channels Based on Particle Method

During nuclear reactor accidents where cooling fails, fuel rod melting and subsequent molten material flow through core channels critically determine disaster progression. Using advanced particle‐based simulation (MPS) with enhanced heat transfer, surface tension, and phase‐change modeling, this study reveals: Zirconium alloy cladding undergoes complex secondary melting, unexpectedly reliquefying after initial solidification when contacting molten fuel material; meanwhile, fuel pellet melting slows after outflow while cladding degradation accelerates due to heat shifts between materials. In multirod (2 × 2) bundles, cladding melts significantly faster with less fuel resolidification due to concentrated heat from additional pellets. Crucially, initial melt volume and temperature dominate relocation behavior: larger melt amounts reduce solidification while intensifying cladding damage, whereas cooler melts increase solidification but maintain severe cladding erosion through prolonged viscous adhesion. This study establishes a critical foundation for advancing fundamental understanding of severe accident progression and expanding the application of the MPS method in nuclear safety.