Dynamic Simulation of Debris Bed Melting Process during the Hypothetical Severe Accident of HPR1000
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摘要: 在核反应堆严重事故后期，压力容器下封头内碎片床熔化对内部传热特性、壁面热流密度和壁面消熔都具有重要影响。本研究基于ANSYS Fluent软件，采用相变模型和大涡模拟（LES）湍流模型对华龙一号（HPR1000）反应堆假想事故下碎片床熔化的动态过程进行了研究，预测了熔池形成过程的温度分布、速度场及壁面消熔的变化规律。结果表明，碎片床熔化开始后，升温速率降低，并逐渐趋于稳定；熔池温度逐渐呈现中上部相对均匀、底部具有较大温度梯度的分布规律，并且随着衰变热功率的增加，熔池温度均匀分布区域向底部扩展；壁面热流密度低于相应位置外部冷却的临界热流密度（CHF）；但是壁面仍然出现了消熔现象，消熔最早出现在壁面内侧靠近碎片床上表面的位置，并逐渐向下扩展，消熔区域范围和深度随停堆后碎片床干涸时间的缩短而增加。本文计算结果可为碎片床相变传热和压力容器完整性研究提供参考。
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关键词:
- 华龙一号(HPR1000) /
- 严重事故 /
- 碎片床 /
- 熔池
Abstract: At the late-phase of nuclear reactor severe accident, the melting process of debris bed in the reactor pressure vessel (RPV) lower head has significant impact on internal heat transfer characteristics, heat flux distribution on vessel wall and vessel wall ablation. In this study, based on the Ansys Fluent, the phase change model and large eddy simulation (LES) turbulence model were used to study the dynamic melting process of debris bed during the hypothetical severe accident of Hua-long pressurized reactor 1000 (HPR1000). The variations of temperature distribution, velocity field and wall ablation during the molten pool formation were predicted. The results showed that the heating rate decreased and tended to be stable after the melting of the debris bed began. The temperature distribution in the pool gradually became relatively uniform in the middle and upper parts, with a large temperature gradient at the bottom. With the increase of the decay heat, the pool part with uniform temperature expanded downward. Although the heat flux distribution on the wall inside was lower than the critical heat flux (CHF) at the corresponding outer position, wall ablation was still observed. The ablation first occurred on the inside of the wall near the surface of the debris bed and gradually spread downward. The area and depth of the ablation increased with the shortening of the debris dry-out time since reactor shutdown. The calculation results here can provide reference for the study of phase change heat transfer in the debris bed and the integrity of the RPV.-
Key words:
- HPR1000 /
- Severe accident /
- Debris bed /
- Molten pool
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图 1 熔池最大温度随时间变化对比图
Figure 1. Comparison of Variation of Maximum Molten Pool Temperature with Time
图 4 不同时间下碎片床中心线温度分布
Figure 4. Centerline Temperature Distribution of Debris Bed at Different Time
图 7 初始工况为停堆后不同时间的碎片床熔化过程中心温度变化规律（衰变热与散热达到平衡的工况点）
Figure 7. Variation of Centerline Temperature Profiles of Debris Bed for Initial Conditions at Different Time Since Reactor Shutdown (Point at Decay Heat Equals to Heat Rejected)
图 8 初始工况为停堆后不同时间的碎片床熔化过程熔池速度流线图
Figure 8. Velocity Streamline Fields of Debris Bed for Initial Conditions at Different Time Since Reactor Shutdown
图 9 初始工况为停堆后不同时间的碎片床熔化过程液相率云图
Figure 9. Liquid Fraction Contours of Debris Bed and Vessel for Initial Conditions at Different Time Since Reactor Shutdown
图 10 初始工况为停堆后不同时间的碎片床熔化过程壁面热流密度与CHF变化规律
Figure 10. Variation of Angular Heat Flux and CHF Distributions Along the Vessel Wall for Initial Conditions at Different Time Since Reactor Shutdown
表 1 模拟采用的碎片床物性参数
Table 1. Debris Bed Properties Employed in Simulation
物性 数值 密度/ (kg·m−3) 7858.27 比热(固体碎片/液态熔融物)/ (J·kg−1·K−1) 496.76/549.45 导热系数(固体碎片/液态熔融物)/ (W·m−1·K−1) 4.50/9.46 熔融物热膨胀系数/K−1 0.007359 固相线温度/K 2319.6 液相线温度/K 2718.4 
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