Abstract：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 microscopy, 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.
2012, Vol. 30 
