Abstract
To develop non-destructive evaluation methods for oxidation damage on graphite components in High Temperature Gas-cooled Reactors (HTGRs), the applicability of ultrasonic wave and micro-indentation methods were investigated. Fine-grained isotropic graphites of IG-110 and IG-430, candidates for Very High Temperature reactor (VHTR), were used. Uniform oxidation condition of these graphites was given by air at 500^0C. The followings were obtained from this study. (1) Ultrasonic wave velocities with 1 MHz in the graphite samples were decreased with increasing the oxidation. For the IG-110 and IG-430, it can be expressed empirically by exponential formulas to burn-off, oxidation weight loss. (2) A wave propagation analysis with a wave-pore interaction model showed slightly less velocity reduction than experimental data of the oxidized IG-110. It implies uniform oxidation assumption in the analysis would not be precisely applicable. The possibility of the effect of the non-uniform oxidation such as un-unique pore growth and grain boundary oxidation was suggested. (3) Micro-indentation characteristics with the maximum indentation load of 10, 25 and 50 N on the graphite samples were changed to show oxidation-induced degradation. It is necessary to assess the variation of the test data with statistic method to specify the oxidation damage in the next study.
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