核级石墨氧化后孔隙结构表征

Characterization of Porosity Development in Oxidized Nuclear Graphite

高温气冷堆是第4代先进核能系统的候选堆型之一,核级石墨作为高温气冷堆重要的中子慢化剂、反射层和结构材料,对于保证反应堆的安全运行和完整性至关重要。核级石墨的氧化会引起其内部孔隙结构的变化,从而对其力学、热学、辐照等性能产生影响。本文介绍了定量描述核级石墨氧化后孔隙结构特征的参量,包括孔隙率、失重率、孔径及BET面积等。系统地总结了国内外用于核级石墨氧化后微观结构表征的常用方法和应用现状,包括直接测量方法和间接测量方法两大类,前者主要有质量-体积法、压汞法、气体吸附法等,后者主要有光学显微成像、X射线成像、显微CT技术、超声波法等;讨论了各种方法和技术的工作原理、应用范围和优缺点,并对核级石墨氧化后的性能研究进行了展望。

The High Temperature Gas-cooled Reactor （HTGR） is one of the candidates for the next generation nuclear power plants. A huge amount of nuclear graphite is used to serve as the neutron moderator, the reflector and the structural materials in the HTGR. However the graphite＇s thermal and mechanical properties will be degraded in the oxidation process caused either by the oxidizing impurities in the coolant or the air ingress accident. The change of the pore structure inside the graphite materials is believed to be the key reason for this degradation. Parameters for characterizing the oxidized graphite＇s pore structure include the porosity, the burn-off degree, the pore size distribution and the BET surface area. The methods and applications in the characterization of the porosity structural development in the oxidized nuclear graphite are systematically discussed, including the direct-method and the indirect- method. The former includes the mass-volume method, the Hg porosimetry, the gas adsorption method, etc; while the latter includes the optical image method, the X-ray radiography, the micro CT, the ultra-sonic microscopy, the electron micr3scopy, etc. The limitations, the advantages and disadvantages of these methods are discussed. With the development of the microscopy and the computer techniques, the computer-aided microscopy will become an effective and powerful tool to characterize the pore development of the oxidized nuclear graphite.