核电牺牲混凝土制备与作用机理研究

Sacrificial concrete, an important component material of core catcher for nuclear reactor, could avoid core melt under extremely high temperature melting wear for pressure vessel, and could prevent the melt and radioactive substances from leaking to the external environment, which will lead to serious social disaster. At present, the melting reaction mechanism on Molten core-concrete interaction (MCCI) and the action mechanism of sacrificial concrete is still constant exploration and requires more scientific analysis and experimental demonstration. In this project, the MCCI process was modeled to reveal interaction mechanism of the melt substances and sacrificial concrete. The quantitative relationship between temperature, density, and the amount of gas generated as for as the core melt and concrete reaction was established and a new designs of sacrificial concrete and its chemical composition was further proposed to prepare to meet the heap pit area and the expansion area require. A series of simulation tests on the melt substances and concrete interaction were carried out to determine characteristic variables such as the interface temperature，the heat transfer coefficient , the rate and ablation depth ablation rate, gas release rate and amount during the interaction between the melt substances and concrete reaction, and so on to reveal the influence of concrete ablation temperature and its type, molten pool shape, the concrete thickness in heap pit underlying and so on, on MCCI model , which could make design parameters and reasonable thickness of sacrificial concrete further optimize.

牺牲混凝土是核电堆芯捕集器的重要组成材料，能够避免高温的堆芯熔融物将压力容器熔穿，防止熔融物和放射性物质泄漏到外部环境中。目前，国内外对堆芯熔融物与牺牲混凝土反应（MCCI）发生熔化的反应机制以及牺牲混凝土的作用机理仍处在不断探索过程中，还需要大量的科学分析和试验论证。本项目将对MCCI过程进行建模，揭示熔融物与牺牲混凝土相互作用机理；建立堆芯熔融物与混凝土反应之间的温度、密度、气体生成量之间的定量关系，提出牺牲混凝土的设计方法，制备出用于堆坑区和扩展区的牺牲混凝土；开展熔融物与混凝土相互作用的模拟试验，来确定建模过程所需的界面温度、热传递系数等特征变量，以及相互作用过程中熔蚀速率、熔蚀深度、气体释放速率和释放量等关键性能参数，来修正严重核电事故的MCCI模型；揭示混凝土熔蚀温度与类型、熔池模型、堆坑底层混凝土厚度等对MCCI的影响规律，进一步优化牺牲混凝土的化学组成、设计参数和结构厚度。

核电是一种低碳能源，也是我国未来能源可持续发展的重要基础。牺牲混凝土是欧洲压水反应堆的重要组成部分，该种反应堆是世界上第三代核电技术的代表，该技术的一个重大革新之处在于通过牺牲混凝土的作用，使核电站在严重核事故中对公共与环境安全性更高。. 本项目研发出利用中、高品位铁矿石和石英石制备硅铁和硅质两种不同类型的核电牺牲混凝土，研究了核电牺牲混凝土高温力学性能演化规律，并利用DSC、SEM、MIP技术分析揭示了高温性能演变机理；试验研究了牺牲混凝土与模拟高温熔融物作用过程中混凝土外观、熔蚀深度和熔蚀速率的变化，并通过XRF、XRD分析揭示了MCCI过程中熔融物与混凝土的混合与反应情况；通过MELCOR程序计算分析了牺牲混凝土分解产生的氧化物是否参与化学反应、混凝土熔蚀焓、混凝土中Fe2O3和H2O含量对MCCI相关现象的影响规律。. 此外，本项目还制备出了性能更为优良的石墨烯改性牺牲混凝土。探究了石墨烯改性牺牲混凝土的高温性能，采用新型实验装置，测量了其高温中力学性能。研究了高温作用下石墨烯改性牺牲混凝土热工参数变化规律，并且揭示了高温作用下其热工参数变化机理。采用超声波检测技术，得到不同温度作用下牺牲混凝土试件的超声波波速。根据损伤定义和应力波理论，得到牺牲混凝土损伤与其超声波波速之间的关系，最终建立了不同温度作用下牺牲混凝土的损伤演化模型。开发了高温作用下牺牲混凝土内部蒸汽压力和温度实时测量装置，采用该装置测量了其内部蒸汽压力和温度；基于上述实验结果，根据细观力学构建了一个牺牲混凝土粘弹性热膨胀模型。本项目还通过数值建模研究了牺牲混凝土的热工参数（热传导系数、分解焓变）对MCCI过程的影响。