Thermal property represents a critical metric when evaluating the performance of next generation nuclear graphite. Despite the extensive measurement data available, a detailed investigation into the influence of microstructure on graphite’s thermal conductivity remains underexplored. In this work, taking advantage of the distinct microstructures between different graphite grades, a comparative study of four graphite grades was conducted to elucidate the structure–property relationship. The microstructures of graphite were characterized by Raman spectroscopy and X-ray diffraction techniques, demonstrating specimen preparation induced damage and annealing induced restoration. Thermal properties were investigated across multiple scales using laser flash analysis and photothermal radiometry. The results indicate that despite similar densities, thermal conductivity varies significantly between different grades and correlates positively with crystallite sizes. By interpolating an infinitely large crystallite and removing the impact of macroscale porosity, an upper bound for the thermal conductivity of isotropic defect-free nuclear graphite has been established.

A comparative study of microstructures and thermal conductivities of nuclear graphite
    Abstract
    1 Introduction
    2 Methods
        2.1 Specimen preparation and thermal annealing
        2.2 Microstructural characterization
        2.3 Thermal diffusivity measurement
    3 Results and discussion
        3.1 Graphite microstructure
            3.1.1 Raman spectroscopy
            3.1.2 X-ray diffraction
        3.2 Thermal properties
        3.3 Impact of microstructures on graphite thermal transport
            3.3.1 Impact of porosity
            3.3.2 Impact of crystallite size
    4 Conclusion
    Acknowledgements 
    References

• Yibo Zhang(Sino‑French Institute of Nuclear Engineering and Technology, Sun Yat-Senen University, Zhuhai 519082, Guangdong, China)
• Qian Liao(Sino‑French Institute of Nuclear Engineering and Technology, Sun Yat-Senen University, Zhuhai 519082, Guangdong, China)
• Xianfeng Ma(Sino‑French Institute of Nuclear Engineering and Technology, Sun Yat-Senen University, Zhuhai 519082, Guangdong, China)
• Yuzhou Wang(Sino‑French Institute of Nuclear Engineering and Technology, Sun Yat-Senen University, Zhuhai 519082, Guangdong, China) Corresponding author
• Derek Tsang(Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China)
• Xu Qiao(Center for Neutron Science and Technology, Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices, School of Physics, Sun Yat-Sen University, Guangzhou 510275, China)
• Vinay Chauhan(Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA)