Study on Reactivity Change Caused by Dynamic Impact of Space Nuclear Reactor
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摘要: 精确计算撞击引入的反应性变化是微型反应堆设计和安全分析中亟待解决的关键问题。本文基于非结构网格蒙特卡罗的中子输运与显式有限元动力学仿真理论，研究在动力学冲击这种大变形条件下的微型反应堆的多物理耦合计算，以85棒束的NaK冷却的空间核反应堆为例，分析了垂直和45°倾角撞击地面过程中的反应性随时间的变化规律。结果表明，在不考虑流体和燃料均匀密度变化条件下，垂直撞击引起的有效增殖系数keff增加约8%，45°撞击引起的keff增加约3%，与文献结果符合较好；而在燃料非均匀密度变化条件下的2种场景keff增加分别提升约10%和20%。上述研究将为空间核反应堆发射的临界安全分析奠定重要的理论基础。Abstract: Accurate calculation of reactivity changes caused by impact is a key problem to be solved urgently in the design and safety analysis of micro-reactors. In this paper, neutron transport simulation and explicit finite element dynamics simulation based on unstructured-mesh Monte Carlo are combined to study the multi-physical coupling calculation of micro-reactor under the condition of large deformation of dynamic impact. Taking the 85-pin NaK-cooled space nuclear reactor as an example, the time-dependent variation of reactivity in the process of vertical and 45° dip impact is analyzed. The results show that, without considering the uniform density change of fluid and fuel, the keff caused by vertical impact increases by about 8%, while the keff caused by 45° impact increases by about 3%, which were in good agreement with the results in the literature. Under the condition of non-uniform fuel density change, the increase of keff in the two scenarios increased by about 10% and 20%, respectively. The research provides an important theoretical foundation for the critical safety analysis of the space nuclear reactor’s launch.
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Key words:
- Micro-reactor /
- Dynamic shock /
- Large deformation /
- Critical characteristics /
- Multi-physical coupling
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图 1 MCNP、DAGMC与ABAQUS耦合流程图
Figure 1. Flow Chart of the Coupling of MCNP, DAGMC and ABAQUS
图 5 垂直跌落前后反应堆几何结构
Figure 5. Reactor Geometry Structure before and after Vertical Impact
图 6 垂直跌落前后的中子注量率归一化分布
Figure 6. Normalized Neutron Flux Rate Distribution before and after Vertical Impact
图 7 垂直跌落特征值和燃料区均匀密度随时间的变化
Figure 7. Variation of keff and Fuel Uniform Density with Time for Vertical Impact
图 8 垂直碰撞末尾时刻燃料区非均匀密度分布
Figure 8. Non-uniform Density Distribution of Fuel Change at the End of Vertical Impact
图 11 45°倾角跌落碰撞前后中子注量率归一化分布
Figure 11. Normalized Neutron Flux Rate Distribution before and after 45° Impact
图 12 45°倾角跌落过程中特征值和燃料区均匀密度变化情况
Figure 12. Variation of keff and Fuel Uniform Density with Time for 45° Impact
图 13 45°倾角跌落末尾时刻燃料区非均匀密度分布
Figure 13. Non-uniform Fuel Density Distribution at the End of 45° Impact
表 1 NaK反应堆堆芯参数
Table 1. Parameters of NaK Reactor Core
参数名 参数值 参数名 参数值 燃料棒数/根 85 燃料UO2密度/(g·cm−3) 9.873 燃料棒长度/cm 38 轴向反射层BeO密度/(g·cm−3) 2.85 燃料棒间距/cm 2.372 径向反射层Be密度/(g·cm−3) 1.85 燃料棒直径/cm 2 包壳SS316密度/(g·cm−3) 7.91 包壳厚度/cm 0.1 吸收体B4C密度/(g·cm−3) 2.52 反射层厚度/cm 15.3 围板SS316密度/(g·cm−3) 7.91 控制鼓直径/cm 15.7 压力容器SS316密度/(g·cm−3) 7.91 控制元件B4C厚度/cm 1.5 水箱容器SS316密度/(g·cm−3) 7.91 
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表 2 UM与CSG几何下冷态临界keff的对比
Table 2. Comparison of Cold Critical keff between UM and CSG
堆芯状态 建模方式 keff 与CSG偏差 控制鼓面向堆芯 MCNP-CSG 0.87310 MCNP-UM 0.87439 129pcm DAG-OpenMC 0.87209 101pcm
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表 3 垂直碰撞末尾时刻不同处理方式下特征值变化的对比
Table 3. Comparison of Different keff Changes at the End of Vertical Impact
参数 不考虑密度变化 均匀密度变化 非均匀密度变化 Δkeff/pcm +140 +7993 +8800
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表 4 45°倾角跌落末尾时刻不同处理方式特征值对比
Table 4. Comparison of Different keff Changes at the End of 45° Impact
参数 不考虑密度 均匀密度变化 非均匀密度变化 Δkeff /pcm −2276 +3090 +3690
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