钠冷快堆堆芯熔融物与液态金属钠作用碎裂机理研究

Fragmentation characteristics of molten corium and sodium interaction have significant influence on the coolability of the corium and the integrity of the primary reactor vessel in the core-melt accident of sodium cooled fast reactor. And heat transfer characteristics of sodium and water exist in significantly difference due to the small Prandtl number of sodium, which causes that the fragmentation mechanism of molten corium and water interaction could not be used to explain the fragmentation mechanism of molten corium and sodium interaction. At present, research on fragmentation mechanism of molten corium and sodium interaction is still in the exploration stage at home and abroad. In this project, fundamental experiments and theoretical researches on fragmentation characteristics and mechanism of molten corium and sodium interaction in sodium cooled fast reactor will be carried out. This project will reveal fragmentation characteristics and mechanism of molten corium with complex multi-component core materials and multiple factors. The key database of fragmentation characteristics of molten corium and sodium interaction will be established, and fragmentation mechanism models of molten corium and sodium interaction will be developed. And the characteristics of energy release and mechanical energy will be obtained during the interaction between molten corium and sodium in sodium cooled fast reactor. This project can possess important scientific significance and engineering reference value for the safety analysis, assessment and verification of sodium cooled faster reactor.

钠冷快堆发生堆芯熔化事故后，堆芯熔融物与液态金属钠作用碎裂特性对熔融物冷却及堆主容器完整性有重要影响。鉴于钠的低Prandtl数使其与水的传热特性存在很大差异，使得熔融物与水作用碎裂机理无法解释熔融物在液钠中的碎裂行为，目前国内外针对堆芯熔融物与液态金属钠作用碎裂机理的研究仍处于探索阶段。本项目着力开展钠冷快堆堆芯熔融物与液态金属钠作用碎裂特性和机理的基础实验和理论研究，揭示复杂多成分堆芯材料、多影响因素下熔融物碎裂特性及机理，研发堆芯熔融物与液态金属钠作用碎裂特性的关键数据库，开发堆芯熔融物在液钠中的碎裂机理分析模型，获得钠冷快堆堆芯熔融物与液态金属钠作用时产生的能量释放和机械能特性。本项目对钠冷快堆安全分析、评估及验证具有重要的科学意义和工程参考价值。

在钠冷快堆严重事故下，堆芯熔融物在液态金属钠中碎裂并凝固形成熔融物碎片，在堆芯捕集器或下封头内重定位形成堆芯碎片床，其形成和冷却特性直接关乎堆芯碎片床再熔化以及再临界事故发生的可能性。然而，对堆芯熔融物射流碎裂现象认知不足，至今未有广泛认可和应用的机理和模型，也缺乏接近于真实事故条件下的熔融物射流碎裂特性研究数据。本项目针对钠冷快堆堆芯熔融物与液态金属钠作用碎裂机理开展了系统的实验、理论及数值模拟方法研究。首先对COSA实验台架进行了改造，添加了熔融物射流初始速度测量装置以及瞬间压力冲击波测量装置，并基于改造后的COSA实验台架开展了不同熔融物物性参数、熔融物射流直径、熔融物初始过热度和液态金属钠初始过冷度对熔融物与液态金属钠作用碎裂机制的影响实验研究；之后基于线性稳定性理论、运动学方程和交界面修正拉普拉斯定律，推导出考虑沸腾和凝固效应的熔融物射流表面不稳定性增长方程，建立了液态金属钠中熔融物射流碎裂模型，并提出了典型环境中熔融物射流碎裂准则；最后建立了一种CFD-DEM耦合数值计算模型以模拟熔融物碎片流在液态金属钠中的重定位行为，通过实验数据验证了模型的正确性，并研究了熔融物碎片直径对碎片流冷却特性和碎片床形态结构的影响。本项目建立的熔融物射流初始速度测量装置、瞬间压力冲击波测量装置、堆芯熔融物与液态金属钠作用碎裂特性的关键数据库、液态金属钠中熔融物射流碎裂模型、CFD-DEM耦合数值计算模型等原创性成果可以为钠冷快堆安全分析、评估及验证提供理论和数据支撑，同时对钠冷快堆堆芯捕集器的设计和布置方案具有重要的科学意义和工程参考价值。