利用时域热反射技术研究离子辐照下石墨晶体的各向异性热输运性质

Graphite serves as the structural component in the core of the high-temperature gas-cooled reactor. It is of great importance to study the radiation effect on the thermal conductivity of nuclear graphite. Graphite crystals have highly anisotropic thermal transport properties, but it is difficult to directly measure the anisotropic thermal conductivity of graphite single crystals because of the limitations of thermal measurement techniques. At present, to study the radiation effect on thermal properties of graphite, the only way is to measure the macro thermal conductivity of polycrystalline graphite by irradiating nuclear graphite blocks with fast neutrons. However, in this project, the variable spot size time-domain thermoreflectance technology will be utilized to achieve the direct measurement of the anisotropic thermal conductivity of graphite single crystal at the microscopic scale. Irradiation of graphite crystals with high-energy ions will be carried out to study the radiation effects on the thermal transport properties of graphite, which improves the database of nuclear-level irradiation effects of graphite. By controlling the defects structure, it is possible to investigate the characterization method for each type of defects in graphite. Furthermore, point defects in terms of interstitial carbon atoms, are covalently linked to adjacent graphite basal planes, and is considered to enhance the cross-plane thermal conductivity of graphite. The role of interstitial atoms will be explored in detail in the current project. The completion of this project will establish the intrinsic heat transport properties of graphite crystals and their radiation effects, not only to solve the fundamental scientific issues related to the thermal transport properties of two-dimensional graphite crystal, but also pave the way to understand the thermal property degradation of polycrystalline nuclear graphite.

石墨是高温气冷堆内重要的堆芯结构材料，研究核级石墨的导热性质在辐照条件下的变化具有十分重要的意义。石墨晶体具有高度各向异性热导率，但由于热测量技术的局限，研究辐照下石墨单晶的各向异性热导率十分困难，目前只能通过快中子辐照多晶石墨块体，然后对多晶石墨的宏观热导率进行讨论。本课题将利用变光斑尺寸时域热反射技术，实现在微观尺度上对石墨单晶各向异性热导率的直接测量。并以高能离子辐照模拟中子辐照，研究辐照下石墨单晶各向异性热输运性质的变化，完善石墨辐照效应数据库。调控辐照缺陷形态，研究不同类型缺陷的结构和识别方法。点缺陷，如间隙碳原子，通常以共价键连接相邻的石墨片层，重点研究间隙碳原子对石墨晶体纵向热导率可能的增强作用，揭示其背后机理。本课题的完成将建立石墨晶体的本征热输运性质及其辐照效应规律，不仅能够解决与石墨(单)晶体热输运性质有关的材料学基本科学问题，还可为多晶核级石墨辐照性能的评价提供铺垫。

石墨是高温气冷堆内重要的堆芯结构材料。石墨晶体具有高度各向异性的热输运性质，辐照下石墨热输运性质的变化规律是反应堆设计与安全性评估的重要依据，目前对石墨晶体热导率的辐照效应还缺乏全面的认识。本项目利用时域热反射技术，在离子辐照高定向热解石墨内部，实现了微观尺度上石墨晶体各向异性热导率的直接测量，并对存间隙碳原子缺陷情况下石墨热导率的物理机制开展了第一性原理计算研究。项目取得的主要研究成果如下：建立了辐照对石墨晶体各向异性热导率的影响规律，揭示了辐照缺陷对石墨纵向热导率的增强作用机理；建立了石墨辐照缺陷的电子显微学表征方法；建立了通过离子辐照，确定石墨晶体尺寸变化的实验方法。相关成果在国内外期刊发表学术论文共3篇，其中包括Carbon一篇，部分核心成果尚未公开发表。培养硕士研究生3名。本项目的完成形成了石墨辐照缺陷研究方法，将对后续石墨缺陷研究的开展打下基础；此外，建立了石墨热导率的辐照效应规律，扩充了石墨的物理学理论，并为核级石墨在反应堆中的应用提供了更好的理论支持。