新型SrFe12O19基核电牺牲混凝土制备及作用机理研究

The safety problem of nuclear power is becoming increasingly acute on a global scale. Sacrificial concrete is the hotspot but also a difficulty in the modern nuclear technology. Sacrificial concrete, as a key component of core catcher in nuclear power plant, is designed to reduce the leakage potential of radioactive materials in severe nuclear accident. Sacrificial concrete can melt and mix with corium (a molten mixture of fuel material, partially or totally oxidized cladding, non-volatile fission products, and various structural materials), reducing the temperature of corium in severe nuclear accident, and it can also modify the physicochemical properties of the corium in order to enable reliable operation of the core catcher. Currently, investigation findings on the preparation of nuclear sacrificial material are rarely published both at home and abroad, and the melting reaction mechanism between molten core and sacrificial concrete and the action mechanism of sacrificial concrete are still constant exploration and require more scientific analysis and experimental demonstration. In the project, the quantitative relationship between temperature, density, and the amount of gas generated for sacrificial concrete during the core melt and corium was established, based on the action mechanism of sacrificial concrete, and a new SrFe12O19 based sacrificial concrete was developed. On this basis, the microstructure, chemical composition, mechanical properties, ultrasonic pulse velocity, and damage of the SrFe12O19 based sacrificial concrete were comprehensively investigated. An experimental setup was designed to measure the real-time temperature and pore vapour pressure of the new sacrificial concrete subjected to high temperatures, and an in-situ meso-mechanical model was proposed to reveal the damage mechanism of the sacrificial concrete exposure to elevated temperatures. An MCCI analytical model in severe nuclear accident was set up, and the main experimental phenomena of MCCI were systematically studied. According to the ablation rate and temperature variation of the sacrificial material obtained from simulation experiment, the more reasonable heat transfer model and interface model of MCCI were proposed in the project. The project is significant to the theoretical interest and practical applications to improve the safety of nuclear power plant.

全球范围内核电安全问题日益突出。牺牲混凝土作为堆芯捕集器的重要组成材料，能够防止堆芯熔融物和放射性物质泄漏，一直是国内外研究的热点与难点。根据牺牲混凝土的工作机理，得到堆芯熔融物与牺牲混凝土之间的温度、密度、氢气产量之间的定量关系，确定牺牲混凝土中SrFe12O19、自由水等关键组分具体含量，提出新型牺牲混凝土的设计方法，制备出SrFe12O19基新型牺牲混凝土。探究新型牺牲混凝土高温作用前后微观形貌、物相组成、力学性能、超声波波速、损伤变化规律，开发牺牲混凝土内部温度、蒸汽压力实时测量装置，构建牺牲混凝土损伤的原位粘结细观力学模型，揭示牺牲混凝土高温作用下损伤劣化机理。建立MCCI数值分析模型，计算并分析典型严重核电事故序列下MCCI相关的主要现象。结合模拟实验测试所得熔蚀速率与温度变化数据、MCCI界面结构变化以及已有MCCI模型，提出更加合理的MCCI过程中的热量传递模型与界面模型。

核电作为清洁高效能源，为保障电力供应安全和节能减排做出了重要贡献。核电是全球实现碳达峰、碳中和的重要突破口，因为在众多能源中核电的碳排放最低。现在核电技术已经发展到了第三代，第三代技术的革新之处在于利用堆芯捕集器使核电站在严重核事故中，对公共与环境具备更高的安全性，而牺牲材料是堆芯捕集器的关键组分。在调整堆芯熔融物的成分和堆芯熔融物的冷却固化过程中，牺牲材料起到了至关重要的作用。.本项目采用HSC Chemistry软件计算牺牲材料与堆芯熔融相互作用（MCCI）体系内各个化学反应的化学反应热、焓变、吉布斯自由能，确定MCCI过程中各个化学反应的顺序以及整个系统的能量变化，最终得到将系统中放热与吸热平衡时所需要的牺牲材料组分的关键参数。本项目探究了不同掺量SrFe12O19对牺牲净浆、牺牲砂浆的常温性能和高温性能的影响，确定了SrFe12O19基牺牲材料中SrFe12O19最高掺量；探究了不同温度作用下SrFe12O19基牺牲材料的热工参数（比热、热传导系数、热扩散系数）变化规律，并且揭示了高温作用下其热工参数变化机理；采用超高温激光共聚焦显微镜，测量了SrFe12O19基牺牲材料的的固相线、液相线温度；采用超声波检测技术，得到不同温度作用下SrFe12O19基牺牲材料的超声波波速；根据损伤定义和应力波理论，得到SrFe12O19基牺牲材料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SrFe12O19基牺牲材料的损伤演化模型。最后，本项目还利用MELCOR模拟程序，探究了SrFe12O19基牺牲材料的MCCI过程。.本项目提出了性能更为优良的SrFe12O19基牺牲材料的配合比，得到了在牺牲材料中SrFe12O19的最高掺量为20%的关键参数。通过实验研究，得到锶铁氧体基牺牲材料的固相线温度在1100℃左右，液相线的温度范围是1237℃~ 1342℃。本项目得到的锶铁氧体基牺牲材料的损伤演化规律，能够用于严重事故情况下灾难评估。本项目制备的锶铁氧体基牺牲材料在MCCI过程中的氢气产量远低于现有的研究结果，能明显提升核电站在严重事故情况下的安全性。本项目的研究结果能够指导SrFe12O19基牺牲材料的制备及应用。