Study on Impact Buckling Simulation Analysis Method and Buckling Behavior of Fuel Assembly Spacer Grid
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摘要: 燃料组件定位格架作为反应堆堆芯的重要部件，其动态屈曲行为直接关系着反应堆结构的安全。本文建立了燃料组件定位格架多次重复冲击仿真分析方法，对比了单次简单冲击仿真、多次重复冲击仿真结果与试验结果的差异，讨论了仿真分析方法对格架冲击动态屈曲行为的影响。研究发现：多次重复冲击仿真分析方法能够模拟试验重复冲击的累积变形过程，其仿真结果与试验结果吻合更好；多次重复冲击仿真和试验的冲击力-冲击初速度曲线在屈曲点附近形成屈服平台，屈服平台内回弹系数和冲击动刚度维持稳定，屈服平台后冲击力快速下降，同时回弹速度与回弹系数剧烈变化，单次简单冲击仿真的冲击力和回弹速度在屈曲点后维持稳定并缓慢增长；屈曲前，冲击加速度时程曲线具有近似对称特征，随着冲击初速度的增加，冲击回弹阶段出现“拖尾”，加速度曲线对称性破坏；多次重复冲击仿真和试验的格架屈曲变形表现为以底部横向剪切变形为主的一阶屈曲破坏，单次简单冲击仿真无法准确预测屈曲形态。本文提出的多次重复冲击仿真分析方法能建立更准确的分析模型，并更准确地揭示定位格架屈曲试验中的动态力学行为。Abstract: The fuel assembly spacer grid is a key part of the nuclear reactor and its dynamic buckling behaviors are important to the reactor structural safety. In this paper, the repeated impact simulation analysis method is established for the fuel assembly spacer grid, the differences between the simulation results of single impact and repeated impact and the test results are compared, and the influence of the simulation analysis method on the dynamic buckling behavior of grid impact is discussed. It is found that the simulation analysis method of repeated impact can simulate the cumulative deformation process of repeated impact in the test, and its simulation results are in better agreement with the test results. The impact force-initial velocity curves of the repeated impact simulation and the test form a yield platform near the buckling point, and the rebound coefficient and impact dynamic stiffness in the yield platform remain stable. After the yield platform, the impact force rapidly decreases, while the rebound velocity and rebound coefficient undergo drastic changes. However, the impact force and rebound velocity of the single simple impact simulation remain stable and slowly increase after the buckling point. Before buckling, the time history curve of the impact acceleration is approximately symmetrical; as the initial velocity increases, the rebound stage of the acceleration curve tails and makes its symmetry destroyed. The buckling deformation of the grids in the repeated impact simulation and the test is a first-order buckling failure dominated by transverse shear deformation at the bottom, while the buckling shape cannot be accurately predicted by the single simple impact simulation. The repeated impact simulation analysis method proposed in this paper can establish a more accurate analysis model and reveal the dynamic mechanical behavior in the buckling test of spacer grid more accurately.
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Key words:
- Spacer grid /
- Impact buckling /
- Repeat-impact /
- Impact force /
- Rebound coefficient /
- Impact stiffness
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图 1 17×17定位格架冲击屈曲有限元模型及边界条件
Figure 1. Impact Buckling Finite Element Model and Boundary Conditions of 17×17 Spacer Grid
图 4 过盈配合模拟计算的格架等效应力云图
X—纵向条带；Y—水平条带
Figure 4. Von Mises Stress Contour Induced by Interference Fit
图 5 最大冲击力随冲击初速度变化曲线
Figure 5. Variations of Maximum Impact Force with Initial Velocity
图 6 冲击质量块加速度时程
①—压缩；②—钝化；③—回弹；④—分离
Figure 6. Acceleration Time History of the Impact Mass
图 7 回弹速度和回弹系数随冲击初速度变化曲线
Figure 7. Variations of Rebound Velocity and Rebound Coefficient with Initial Velocity
图 8 冲击简谐运动周期计算示意图
Figure 8. Schematic of Period-calculation of Impact Simple Harmonic Motion
表 1 315℃下格架材料力学性能参数
Table 1. Mechanical Parameters of Grid Materials at 315℃
材料 密度/
(kg·m−3)弹性模
量/GPa泊松比 屈服强
度/MPa切线模
量/MPaZr-4 6500 78 0.35 139.3 627.9 Inconel-718 8220 184 0.27 931 4112.3 
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