Study on Evolution Mechanism for Local Melting Accident of Dispersed Plate Fuel
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摘要: 为掌握板状燃料熔化事故演化过程，防止堆芯燃料持续熔化扩展，以典型板状燃料研究堆JRR-3M为对象，采用流体体积（VOF）法与焓-多孔介质法相耦合，对相邻流道堵塞后弥散型板状燃料局部熔化与熔融物迁移过程展开模拟。模拟结果表明：局部熔化事故的演化过程分为升温、熔化、迁移、凝固4个阶段，其中，迁移阶段的时间极短，持续不足3 s，但对事故扩展起决定性影响；迁移阶段，熔融物以底部聚集和中部液滴溅射两种方式迁移至相邻燃料板上，在被相邻燃料板充分冷却后，开始凝固；高温熔融物在接触相邻燃料板后，会导致相邻燃料板冷却壁面的温度迅速上升至500~600 K，远超冷却剂沸点，使相邻燃料板存在被烧毁的风险。该模拟方法与结果可为板状燃料堆芯熔化事故的安全分析提供支持。Abstract: To understand the evolution process of plate fuel melting accident and prevent the continuous core fuel melting, the typical plate fuel research reactor JRR-3M was used as the research object, and the volume of fluid (VOF) method was coupled with enthalpy-porosity method to simulate the local melting and melt migration process of dispersed plate fuel after adjacent flow channels were blocked. The simulation results show that the evolution process of local melting accident is divided into four stages: temperature rise, melting, migration and solidification. Among them, the migration stage is extremely short and lasts less than 3 s, but it has a decisive influence on the accident expansion. In the migration stage, the melt migrates to the adjacent fuel plate in two ways: bottom gathering and middle droplet sputtering, and begins to solidify after being fully cooled by the adjacent fuel plate. After the high-temperature melt contacts the adjacent fuel plate, the temperature of the adjacent fuel plate cooling wall will rise rapidly to 500~600 K, far exceeding the boiling point of the coolant, which poses a burnout risk to the adjacent fuel plate. The established simulation method and the obtained simulation results can provide support for the safety analysis of plate fuel core melting accident.
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Key words:
- Plate fuel /
- Melting accident /
- Evolution mechanism /
- Numerical simulation
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图 1 JRR-3M标准组件几何模型图
y—以燃料组件底部出口为原点的轴向位置；FZ—轴向功率因子。
Figure 1. Geometric Model Diagram of JRR-3M Standard Assembly
图 2 燃料板二维局部熔化分析模型示意图
Figure 2. Schematic Diagram of 2D Local Melting Analysis Model of Plate Fuel
图 3 不同网格量下事故发生后0.1 s的燃料最高温度曲线
Figure 3. Maximum Fuel Temperature Curve at 0.1 s after the Accident under Different Grid Numbers
图 4 不同FR下的燃料最高温度瞬变图
Figure 4. Maximum Temperature Transient Diagram of Fuel under Different FR Values
图 5 FR=2.62工况中不同时刻的熔融物分布云图
Figure 5. Cloud Diagram of Melt Distribution at Different Times in FR=2.62 Condition
图 7 FR=2.62工况中不同时刻下左右两侧的壁面温度分布
Figure 7. Temperature Distribution on the Left and Right Walls at Different Times in FR=2.62 Condition
表 1 包壳与芯体的热物性参数
Table 1. Thermophysical Parameters of Cladding and Core
参数名 参数值 包壳 芯体 密度/(kg·m−3) 2700 6000 比热/(J·kg−1·K−1) 896 406.7 热导率/(W·m−1·K−1) 170 （固相）
100（液相）32（固相）
34 （液相）液相粘性系数/(mPa·s) 2.0 5.6 液相表面张力/(N·m−1) 0.914 0.914 固相线温度/K 855 855 液相线温度/K 925 925 熔化潜热/(kJ·kg−1) 396.7 113.1 
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