高温气冷堆球形燃料元件表面复合涂层的调控设计、性能表征与抗氧化机理研究

Spherical fuel element is the most key core technology of High Temperature Gas-cooled Reactor (HTR), and its performance directly determines the safety and economy of HTR. Impoving the oxidation resistance of fuel element under high temperature and oxidizing environment is very important to increase the operation temperature of spherical fuel element, research and development new type HTR fuel element, and further improve the safety and economy of HTR.. Try to solve the oxidation issue of spherical fuel element substrate graphite, a unique SiC/Si-Zr/ZrC/ZrO2-SiO2 composite coating on the surface of HTR fuel element is proposed in this project. The stability under high temperature oxidizing atmosphere, oxidation behavior and anti-oxidation mechanism of composite coating will be researched, and a new type HTR anti-oxidation spherical fuel element will be developed..First, based on the unique requirements of service environment of spherical fuel element in reactor, thermodynamic method will be taken to analyze the oxidation behavior and high temperature thermal stability of different single layer such as SiC, ZrC, SiO2, ZrO2 under different oxidation environment condition. Then, a novel multilayer coating with different fuctions will be designed based on the above results, the preparation technology be optimized. The changing fuctions between spherical fuel element performance and coating structure, preparation process, and the coating parameters and oxidation conditions of oxidation weight loss rate of the samples will be also researched. To study the high temperature thermal stability and oxidation mechanism of new type composite coating and find new composite coating which can significantly improve the spherical fuel element antioxidant properties. This research has very important theoretical significance and potential application prospect to improve the oxidation resistance performance of spherical fuel element for HTR at high temperature and oxidation ambient.

球形燃料元件是高温气冷堆最关键的核心技术，直接决定了高温气冷堆的安全性和经济性。提高燃料元件在高温氧化性环境中的抗氧化性能对于提高球形燃料元件运行温度，发展新型高温气冷堆燃料元件，改善高温气冷堆的安全性和经济性具有重要的意义。.本项目针对高温气冷堆球形燃料元件的氧化问题，首先根据燃料元件在反应堆内特殊的服役环境要求选择材料体系，并通过对SiC、ZrC、SiO2、ZrO2等单一涂层在不同氧化条件下的氧化行为进行理论分析和实验研究，在球形燃料元件表面设计独特的、具有不同功能的SiC/Si-Zr/ZrC/ZrO2-SiO2复合涂层结构，研究并优化复合涂层的制备工艺，分析球形燃料元件性能与涂层结构、制备工艺之间的变化规律，分析涂层参数和氧化条件对样品氧化失重速率的影响，研究复合涂层在高温氧化气氛下的稳定性、氧化行为和抗氧化机理。研究结果预期将为研制高温气冷堆新型抗氧化球形燃料元件奠定基础。

燃料元件是反应堆的核心技术。其中，石墨占高温气冷堆燃料元件总重量的约97%。在超过500℃的氧化性气氛中，燃料元件的石墨基体发生氧化使其性能下降，一定程度上导致燃料元件的机械性能、结构稳定性下降，对裂变产物的阻挡性能降低，使裂变产物的释放增加等，从而严重影响反应堆的安全性。.本项目采用两步包埋法在石墨球表面制备了微四层结构的SiC复合涂层，并对其在不同条件下的氧化行为进行了详细的研究。实验表明，微四层SiC涂层由纳米级别的内部过渡层和细化晶粒层、微米级别的致密体层和外部疏松层构成。其中，内部过渡层是主要的耐热震功能层，细化晶粒层和致密体层是主要的抗氧化功能层。微四层结构的SiC涂层在静态空气中表现出了极佳的抗氧化效果：在1500℃氧化长达200h之后，品的质量增加仅为0.52%；在1200℃氧化长达1000h之后，样品质量增加仅为0.25%。而在水汽混合条件下，随着水汽浓度的增加，涂层表面的颗粒长大越来越明显，并在颗粒表面出现了台阶状。.本研究中最终制备抗氧化涂层是燃料元件在高温、空气气氛等不同的特殊环境中应用的先决条件，是制备不同尺寸和铀装量的燃料元件的基础，是未来进行更深一步的辐照研究和堆内实际检验的前提。其成功制备可以为进一步研发应用于特殊环境要求的反应堆新型燃料元件奠定基础，使这种新型燃料元件不仅可以用在高温气冷堆，还可以用在熔盐堆、快堆、压水堆、空间堆等。本项目的研究是基于未来具有特殊环境要求的反应堆设计对燃料元件的需求而凝练出的科学问题，其成功解决具有非常重要的理论意义和应用价值。