Analysis of Influence of Expansion on Control Rod Drop in Nuclear Reactor at High Temperature
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摘要: 核反应堆内的高温环境会导致控制棒组件产生热膨胀现象，进而影响控制棒组件的下落时间。为研究热膨胀对控制棒组件下落的影响，建立考虑膨胀变形的控制棒下落流固耦合模型，求解控制棒组件下落过程的动力学方程。采用有限元对导向管和控制棒进行稳态热力耦合分析，得到高温条件下控制棒和导向管的膨胀变形。基于所建立模型比较考虑热膨胀和不考虑热膨胀条件下控制棒的下落动力学过程。分析结果表明，热膨胀现象延迟了控制棒整体下落时间，但对控制棒进入缓冲段入口的时间影响较小，因此在一般情况下热膨胀对落棒时间的影响可以忽略，但在工程中仍需要重视控制棒膨胀引起的后果。本文研究结果对控制棒结构设计以及控制棒堆内落棒时间分析有重要意义。Abstract: The high temperature environment in the nuclear reactor will cause the thermal expansion of the control rod assembly, which will affect the falling time of the control rod assembly. In order to study the effect of thermal expansion on the drop of control rod assemblies, a fluid-structure coupling model for the drop of control rod assemblies was established considering expansion deformation, and the dynamic equations for the drop process of control rod assemblies were solved. The steady state thermodynamic coupling analysis of the guide tube and control rod is performed using finite element method to obtain the expansion deformation of the control rod and guide tube under high temperature conditions. Based on the established analytical model, the dynamic processes of control rod drop with and without expansion is compared. The analysis results show that the thermal expansion phenomenon delays the total drop time of the control rod, but has little impact on the drop time before the buffer section. Therefore, in general, the impact of thermal expansion on the drop time can be ignored, but the consequences caused by the control rod expansion still need to be paid attention to in the engineering design. The conclusion of this paper is important for the design of control rod and the analysis of in-pile control rod drop time.
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Key words:
- Control rod drop /
- Thermal expansion /
- Finite element /
- Fluid-structure coupling
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图 1 控制棒下落热膨胀模型
黄色部分—控制棒向外膨胀部分；P—压强；v—控制棒下落速度
Figure 1. Thermal Expansion Model of Control Rod Drop
图 4 控制棒和导向管的轴向温度分布图
Figure 4. Axial Temperature Distribution of Control Rod and Guide Tube
图 8 不同位置直径变化与轴向坐标关系图
Figure 8. Relationship between Diameter Change at Different Positions and Axial Coordinate
图 9 热膨胀前后控制棒下落过程对比图
Figure 9. Comparison of Rod Drop Processes before and after Expansion
表 1 堆芯结构和流量相关参数
Table 1. Parameters of Core Structure and Flow Rate
参数名 数值 控制棒长度/m 4 控制棒直径/mm 9.7 导向管底部长度/m 0.5 导向管底部内径/mm 10 导向管顶部长度/m 3.5 导向管顶部内径/mm 11.4 侧孔距底部距离/m 0.52 反应堆内每个回路内的流量/(m3·s−1) 1.8×10−3 
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表 2 热膨胀前后落棒时间相对偏差
Table 2. Relative Deviation of Control Rod Time before and after Thermal Expansion
对比项 热膨胀前 热膨胀后 相对偏差 控制棒进入缓冲段时间 1.4270 s 1.4375 s 0.74% 控制棒整体落棒时间 1.8587 s 1.9197 s 3.28%
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