Study on Heat Transfer and Interlayer Crust Characteristics of Two-layer Corium Pool Based on Visualization Experiments
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摘要: 为了研究双层熔融池氧化层与金属层之间的分层界面硬壳形成特性，分析界面硬壳对熔融池流动传热的影响，设计搭建了可视化双层熔融池实验装置。50 mol%NaNO3-50 mol%KNO3混合熔盐与高温导热油分别作为氧化层与金属层的模拟物，熔融池修正瑞利数在109~1012范围内。开展了6组实验，观察到了界面硬壳的动态形成特性，获得了熔融池温度、侧壁面热流密度、硬壳厚度和传热特性关系式，分析了界面硬壳对双层熔融池传热特性的影响。结果表明，界面硬壳从侧壁面开始生长，且形成的界面硬壳将会削弱双层熔融池向上传热，并导致熔融池最高温度出现在界面硬壳下方。本研究解决了双层熔融池界面硬壳生长过程难以观察的问题，总结了界面硬壳状态变化规律，能够为严重事故安全分析提供数据支撑。Abstract: To study the formation characteristics of the interlayer crust between the oxide layer and the metal layer in the two-layer corium pool, and analyze the effect of the interlayer crust on the flow and heat transfer of the corium pool, a two-layer corium pool visualization experimental device was designed and built in this study. 50 mol%NaNO3-50 mol%KNO3 molten salt and high-temperature heat transfer oil were used as simulants of oxide layer and metal layer respectively, and the modified Rayleigh number of corium pool is 109~1012. The study includes six experiments to observe the dynamic formation characteristics of the interlayer crust. The corium pool temperature, sidewall heat flux, crust thickness and heat transfer correlations were obtained, and the impact of the interlayer crust on the heat transfer characteristics in a two-layer corium pool was analyzed. The results indicate that the interlayer crust grows from the side wall and its formation weakens the upward heat transfer in the two-layer corium pool, resulting in the highest temperature in the melt pool below the interlayer crust. This study addresses the challenge of observing the growth process of the interlayer crust in a two-layer corium pool and summarizes the variations in the state of the interlayer crust, providing data support for safety analysis of severe accidents.
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Key words:
- Severe accident /
- Two-layer corium pool /
- Interlayer crust /
- Natural convection
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图 1 实验段电加热棒和热电偶布置示意图 mm
IT—测量熔融池内部温度的热电偶；WT—测量圆弧壁面内外温度的热电偶；CT—测量硬壳温度的多点式热电偶；Φ—试验段直径。
Figure 1. Layout Diagram of Heating Rod and Thermocouple in Experimental Section
图 2 可视化双层熔融池实验回路
蓝线—冷却回路；黄线—气体回路。
Figure 2. Visualized Two-layer Corium Pool Experimental Loop
图 3 熔融池稳态温度分布（工况2）
黑色虚线为分层界面位置，红色虚线为金属层顶部位置，下同。
Figure 3. Temperature Distribution of Corium Pool in Steady State (Case 2)
图 4 稳态熔融池无量纲温度分布
Figure 4. Dimensionless Temperature Distribution of Corium Pool in Steady State
图 5 壁面热流密度稳态分布（工况2）
Figure 5. Heat Flux Distribution on Wall Surface in Steady State (Case 2)
图 6 壁面热流密度稳态分布（工况6）
Figure 6. Heat Flux Distribution on Wall Surface in Steady State (Case 6)
图 10 壁面硬壳厚度稳态分布（工况5）
Figure 10. Crust Thickness Distribution on Wall Surface in Steady State (Case 5)
图 11 分层界面硬壳状态与氧化层高度比例、熔融池功率密度的关系
Figure 11. Relationship between Inter-layer Crust State and Oxide Height Proportion, Corium Pool Power Density
图 12 COPRA-II双层熔融池实验与可视化双层熔融池实验Nuup/Nudn对比
Figure 12. Nuup/Nudn Comparison between COPRA-II Two-layer Corium Pool Test and Visualized Two-layer Corium Pool Test
表 1 实验模拟物物性参数
Table 1. Physical Property Parameters of Experimental Simulant
物性 50 mol% NaNO3-
50 mol% KNO3L-QC310 密度/(kg·m−3) 1964 856.3 运动粘度/(m2·s−1) 2.76×10−6 4.736×10−6 热膨胀系数/K−1 1.05×10−4 0.0008 导热系数/(W·m−1·K−1) 0.48 0.1 比热容/(J·g−1·K−1) 1.29 2.907 普朗特数（Pr） 14.5 112 
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表 2 实验工况表
Table 2. Test Cases
工况 上部边界 氧化层高度/mm 金属层高度/mm 功率/kW 1 辐射 310 2.10/1.40/0.70 2 390 30 2.85/1.90/0.95 3 380 40 2.85/1.90/0.95 4 310 40 2.10/1.40/0.70 5 310 60 2.10/1.40/0.70 6 300 100 2.10/1.40/0.70
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表 3 实验系统测量误差
Table 3. Measurement Uncertainties of Experimental System
测量参数 Δin Δac 不确定度 IT热电偶温度/℃ 0.5 0.36 ±0.497 WT热电偶温度/℃ 0.5 0.36 ±0.497 氧化层高度/m 0.02 ±0.02 金属层高度/m 0.02 ±0.02 WT热电偶间距/m 0.002 ±0.002 平均热流密度 ±2%~5%
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