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采用带移动边界的三维瞬态模型对1/4堆芯模型进行热传导分析.考虑了堆芯熔融物滞留工况下反应堆衰变功率和压力容器内部水位的下降过程,以及不同材料组件在堆内的真实径向分布.棒束表面与冷却剂的自然对流换热采用饱和蒸汽/水经验关系式计算,辐射换热采用相邻16棒间辐射模型计算.建立了动态烧蚀模型以模拟不断累积的堆芯熔融物对下支撑板的烧蚀作用.着重考虑了由熔融物滴落造成的冲击换热以及下支撑板上形成的熔坑底部换热.文献验证对比证明了模型的正确性.模拟结果表明:事故进程2600s时,冷却剂蒸干造成堆芯融化速度急剧加快.8000 s时80％的堆芯质量熔化.下支撑板上的烧蚀区域主要集中于板心半径700 mm处,并在6000s时完全贯穿.“,”To precisely understand the accident process of reactor core melt in In-vessel retention (IVR) condition,3dimensional transient thermal conduction analysis with moving boundary is performed on quarter reactor core model.The decline of decay power and water level in reactor pressure vessel (RPV),and the radial distribution of assemblies of different material is considered.Convective heat transfer on rod surface and coolant interface in computed with empirical correlation of natural convection of saturated steam vapor/water.Radiation heat transfer with 16 neighboring rod is considered.Also,the ablation caused by continuously accumulation of molten corium on lower support plate (LSP) is simulated.The impingement heat transfer of the falling corium and the molten pool formed in LSP ablation cavity is taken into account.The simulation gives the ablation process on the surface of LSP as well as temperature history and molten proportion of the reactor core,which shows agreement with reference.Simulation shows:the melt process of reactor core accelerated in the accident process of 2600 s,when coolant in RPV dry up 65％ of the core mass has molten at 8000 second.LSP is completely penetrated in 6000 s,the ablation of LSP is mainly focused on an annular region of radius 700 mm.