严重事故下压力容器下封头内熔融物凝固相变动态特性研究

The heat transfer characteristics of the melt pool in the reactor pressure vessel (RPV) lower head directly determined the heat flux and the distribution of the heat flux on the RPV wall, which had a significant effect on the IVR strategy. The phase transition dynamics of melt solidification in the RPV lower head under the condition of the severe accident is a current international hot topic..The experimental study and theoretical analysis will be combined to investigate the key phenomena that affected the heat transfer characteristics of the melt pool in the RPV lower head, according to the hot issue of research on the heat transfer characteristics of the large-scale melt pool. In this proposal, the effect of the transient characteristics of the crust solidified by the melt on the diffusion of the melt compositions at the interface of the melt/crust and the interface temperature will be investigate based on the COPRA facility. And the diffusion dynamics model will be developed based on the diffusion boundary layer theory. The inherent law of the phase transition dynamics of melt solidification, the melt compositions diffusion dynamics at the interface, as well as the interface temperature will be obtained through theoretical analysis and experimental study. This proposal can reveal the effect of the phase transition dynamics of melt solidification on the heat transfer characteristics of the large-scale melt pool. The research of this proposal can provide the theoretical support for the research and implement of the IVR strategy under the severe accident for our county large-scale PWR. And this proposal also can accumulate fundamental data and fundamental theory for the research on the heat transfer characteristics of the large-scale melt pool.

严重事故下压力容器下封头内熔融池换热特性直接决定了压力容器壁面热负荷大小及壁面热流密度的分布特性，对IVR策略有着重要的影响。压水堆严重事故下压力容器下封头内熔融物凝固相变动态特性对熔融池换热的影响是目前国际上关注的一个热点问题。.本课题针对大型熔融池换热特性研究方面的热点问题，通过实验研究和理论分析相结合的方法对影响压力容器下封头内熔融池换热特性的关键现象开展基础研究。基于COPRA实验台架研究熔融物凝固形成的硬壳的瞬态特性对固液相界面处熔融物成分扩散特性及相界面温度的影响，并基于扩散边界层理论建立熔融物成分扩散动态特性分析模型，通过理论分析和实验研究掌握熔融物相变特性、相界面成分扩散特性及相界面温度之间的内在规律，揭示熔融物凝固相变动态特性对大型熔融池换热的影响。本项目为我国大型压水堆严重事故下IVR策略的研究和实施提供理论支撑，为大型熔融池换热特性研究积累宝贵的实验数据和基础。

严重事故后堆芯熔化产生的熔融物会在压力容器下封头内形成液态熔融池，熔融池内的流动换热特性直接决定了压力容器壁面热负荷大小及壁面热流密度分布，对IVR策略有着重要的影响。本课题采用实验研究和理论分析相结合的方法，深入探索了熔融池瞬态换热特性及熔融物凝固相变动态特性对大型熔融池换热行为的影响。通过设计和改造COPRA实验台架，获得了压力容器内壁面形成的熔融物硬壳厚度和固液相界面处的熔融物成分，研究了硬壳瞬态特性对熔融物成分扩散过程及相界面温度的作用；基于扩散边界层理论建立了熔融物成分扩散动态特性分析模型，可用于研究相界面成分的瞬态扩散特性及其对相界面温度的影响机制；同时，开发了熔融物凝固相变动态特性数值分析模型，可用于模拟熔融池流动换热特性和熔融物凝固相变特性；最终，借助理论分析和实验研究掌握了熔融物相变特性、相界面成分扩散特性及相界面温度之间的内在规律，揭示熔融物凝固相变动态特性对大型熔融池换热的影响。本项目为我国先进压水堆严重事故下IVR策略的研究和实施提供理论支撑，为大型熔融池换热特性研究积累宝贵的实验数据和基础。