钠冷快堆堆芯捕集器涂层的消熔特性及驱动机制研究

During the severe accidents in sodium-cooled fast reactors, the molten corium will relocate to the lower plenum and accumulate on the core catcher. The interaction between non-eutectic corium and ceramic oxide will lead to the coating dissolution by component diffusion, which will affect the safety performance of core catcher. Due to the obvious deficiencies in the research of coating dissolution dynamics, this project aims to investigate the dynamic characteristics and driving mechanisms of coating dissolution in both experimental and theoretical methods. Some key parameters of dissolution characteristics and corresponding influence factors will be obtained from the sodium nitrate-potassium nitrate simulation experiment under different conditions. Then based on the non-eutectic phase diagram and component diffusion equation, the boundary layer transient evolution with coupled effect of temperature gradient and concentration gradient will be studied. Finally, from the numerical simulation of heat and mass transfer interaction behavior, the driving mechanisms for the coating dissolution by component diffusion will be revealed. It’s expected to achieve innovations in the study of diffusive dissolution dynamics based on the temperature gradient and concentration gradient coupling. The results will serve to evaluate the effectiveness of non-eutectic corium retention by core catcher during the transient and long-term cooling stage. The research can provide experimental data and theoretical support for the safety performance analysis and structure optimization design of core catcher in sodium-cooled fast reactor.

钠冷快堆发生严重事故时，堆芯熔融物会向下腔室迁移堆积在堆芯捕集器上，非共晶熔融物与陶瓷型氧化物之间的相互作用会引起涂层材料以组分扩散形式逐渐消熔，会对堆芯捕集器的安全性能产生明显影响。目前国内外关于涂层消熔动力学特性研究存在明显不足，本项目将针对涂层消熔的动态特性及驱动机制开展实验和理论研究。首先基于硝酸钠-硝酸钾模拟实验获得不同工况下涂层消熔的关键参数及其影响因素，然后依据非共晶相图和组分扩散方程，阐明温度梯度-浓度梯度耦合作用下的边界层瞬态演变规律，最后通过对涂层消熔过程中瞬态传热-扩散传质相互作用行为的数值模拟，揭示边界层组分扩散对涂层消熔的驱动机制。通过本项目的研究，期望在温度梯度-浓度梯度耦合的扩散消熔动力学研究上取得创新成果，评估瞬态及长期冷却阶段堆芯捕集器陶瓷型涂层持留非共晶熔融物的有效性，为钠冷快堆堆芯捕集器的安全性能分析和结构优化设计提供实验数据和理论支持。

钠冷快堆发生严重事故时，堆芯捕集器上堆积的非共晶熔融物与陶瓷型氧化物之间的相互作用会引起涂层材料以组分扩散形式逐渐消熔，会对堆芯捕集器的安全性能产生明显影响。但是目前国内外关于涂层消熔动力学特性研究存在明显不足，本项目采用实验研究、理论分析、数值模拟相结合的方法，全面探讨了非共晶熔融物对涂层消熔过程的传热传质特性。实验研究获得了相界面的瞬态位置、局部温度、组分浓度等关键参数，将涂层消熔过程分为三个阶段：熔融物骤冷凝固及再熔化阶段、涂层组分扩散消熔阶段、消熔终止阶段。依据非共晶熔融物的二元相图建立了温度梯度和浓度梯度的耦合模型，求解获得了相界面温度和浓度的变化规律，解释了熔融物温度低于涂层材料熔点条件下的组分扩散消熔原理。实现了瞬态传热-扩散传质相互作用行为的数值模拟，在熔融池区域、边界层区域和涂层区域分别建立自然对流模型、组分扩散模型和热传导模型。相比于单组分的凝固涂层，采用与熔融物组分相同的凝固硬壳作为涂层材料，能够抑制组分扩散减缓消熔，在严重事故瞬态及长期冷却阶段能够对非共晶熔融物的持留起到更有效的作用。本项目的研究成果能够为钠冷快堆堆芯捕集器的安全性能分析和结构优化设计提供实验数据和理论支持，具有一定科学意义和工程价值。