Numerical Simulation of RPV with Complex Mechanical Behaviors under Core-melting Accident
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摘要: 在反应堆冷却剂丧失事故（LOCA）后，堆芯熔融物将对反应堆压力容器（RPV）下封头产生烧蚀作用，为此模拟和分析在堆芯熔融事故下RPV内壁的烧蚀及复杂力学行为对于RPV的设计、事故预防和缓解都具有重要意义。本文首先给出了近场动力学方法分析含裂纹扩展的热力耦合问题的积分列式。其次，在近场动力学方法框架下，提出了一种简便和高效的移动边界模型。其中，通过引一个标量场来直接表征物质点的烧蚀状态，使得在计算过程中不需要不断地更新计算域，从而提高计算效率。最后，采用该方法模拟了堆芯熔融物对RPV内壁的动态烧蚀和RPV在内压作用下的裂纹扩展，计算结果表明在堆芯熔融事故下RPV中同时存在弹性变形和塑性变形，而且还存在损伤断裂等复杂力学行为。Abstract: After the severe loss of coolant accident (LOCA), the lower head of reactor pressure vessel (RPV) will be ablated by the core melt. Therefore, it is of great significance to simulate and analyze the ablation and complex mechanical behavior of the pressure vessel wall under the condition of core melt for the design, accident prevention and mitigation of RPV. This paper firstly presents the peridynamic formulation of coupling thermo-mechanical problem with crack propagation. Then, based on the peridyanmic framework, a simple and efficient moving boundary model is proposed. The abated status of the material points is directly characterized by introducing a scalar field, which makes it unnecessary to constantly update the calculation domain in the calculation process, thus improving the calculation efficiency. Finally, the present method is used to simulate the dynamic ablation of the core melt on the pressure vessel wall and the crack propagation of the pressure vessel under the action of internal pressure. The calculation results show that there are both elastic deformation and plastic deformation in RPV under the core melt accident, and there are also complex mechanical behaviors such as damage and fracture.
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Key words:
- Peridynamics /
- Coupling thermo-mechanics /
- Ablation /
- Moving boundary /
- Numerical simulation
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图 2 RPV下封头高温烧蚀计算模型
θ—与中轴线夹角；H—熔融物厚度；下标M—金属熔池；下标U—铀氧化物熔池；下标V—RPV
Figure 2. Computational Model of RPV Lower Head for Thermal Ablation
图 3 施加在RPV内壁上的热流密度随几何角度的变化
Figure 3. Variation of Heat Flux Imposed on the RPV Inner Wall with the Angles
图 4 热烧蚀作用下RPV移动的内壁轮廓
Figure 4. Profile of the Moving Inner Wall of RPV Caused by Thermal Ablation
图 5 不同时刻RPV温度和烧蚀形状分布图
Figure 5. Temperature Contours and Ablated Shapes of RPV at Different Times
图 6 弹性分析条件下截面路径上等效Mises应力和温度分布
Figure 6. Curves of Mises Stresses and Temperature Distribution for the Given Path under Elastic Condition
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