空间核反应堆动力学冲击引起的反应性变化研究

Study on Reactivity Change Caused by Dynamic Impact of Space Nuclear Reactor

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k_(eff)增加约8%,45°撞击引起的k_(eff)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k_(eff)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。

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 k_(eff) caused by vertical impact increases by about 8%,while the k_(eff) 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 k_(eff) 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.