事故容错燃料碳化硅包壳表面临界热流密度特性机理研究

The accident tolerant fuel (ATF) is a new generation of fuel system, designed for improving the ability against the serous accident of fuel elements. As a main candidate cladding materials, the critical heat flux (CHF) characteristics of silicon carbide (SiC) claddings play an important role in the design and safety analysis of ATF. However, the research on CHF mechanisms of SiC claddings in ATF is still in the exploration stage at home and abroad. In this project, experimental and theoretical researches on CHF mechanism of SiC claddings in ATF will be carried out. Firstly, based on the obtained influence mechanisms of coating thickness, wall roughness, surface wettability, and coating oxide layer on CHF of SiC-coated surface, the main variables are determined. Then, the steam-water interfacial behavior near the dry spot and the dynamic evolution mechanism of liquid microlayer on the SiC-coated surface were illuminated when CHF occurs. Additionally, the boiling crisis criteria will be obtained. Then, based on the CHF influence mechanisms, experimental data and the boiling crisis criteria, the CHF theoretical model of SiC-coated cladding in ATF will be built. Lastly, the safety performances of the present Zircaloy cladding and new SiC-coated cladding under serious accidents will be evaluated. This project can provide important experimental data and theoretical support for the optimum design and safety analysis of ATF.

事故容错燃料是为提高燃料元件抵御严重事故能力而开发的新一代燃料系统，碳化硅作为主要候选包壳材料，其表面临界热流密度特性对事故容错燃料的设计和安全分析至关重要，然而目前国内外针对该问题的研究仍处于探索阶段。本项目将开展事故容错燃料碳化硅包壳表面临界热流密度特性试验和理论研究，主要完成：首先，基于机理性试验阐明涂层厚度、表面粗糙度、壁面润湿性和涂层氧化物等参数对碳化硅涂层表面临界热流密度的影响机理，提炼临界热流密度主要影响变量；其次，揭示沸腾临界时碳化硅涂层表面蒸干点附近汽液界面行为规律和微液层动态演变机理，制定沸腾临界发生判据；最后，基于临界热流密度影响机理、试验数据和沸腾临界发生判据，建立事故容错燃料碳化硅包壳表面临界热流密度理论模型，评价新一代碳化硅涂层包壳和现有核燃料锆合金包壳在反应堆严重事故下的安全性能。课题研究成果将为事故容错燃料的优化设计与安全性能分析提供重要试验数据和理论支撑。

事故容错燃料是为提高燃料元件抵御严重事故能力而开发的新一代燃料系统，碳化硅作为主要候选包壳材料，其表面临界热流密度特性对事故容错燃料的设计和安全分析至关重要，然而目前国内外针对该问题的研究仍处于探索阶段。本项目开展了事故容错燃料碳化硅包壳表面临界热流密度特性试验和理论研究，主要完成了以下工作：首先，基于机理性试验阐明涂层厚度、表面粗糙度、壁面润湿性和涂层氧化物等参数对碳化硅涂层表面临界热流密度的影响机理，提炼临界热流密度主要影响变量；其次，揭示沸腾临界时碳化硅涂层表面蒸干点附近汽液界面行为规律和微液层动态演变机理，制定沸腾临界发生判据；最后，基于临界热流密度影响机理、试验数据和沸腾临界发生据，建立事故容错燃料碳化硅包壳表面临界热流密度理论模型，评价新一代碳化硅涂层包壳和现有核燃料锆合金包壳在反应堆严重事故下的安全性能。课题研究成果将为事故容错燃料的优化设计与安全性能分析提供重要试验数据和理论支撑。