Irradiation creep properties and strength of a fine-grained isotropic graphite

Abstract

An irradiation creep test was conducted on a fine-grained isotropic graphite, IG-110, for the high temperature gas-cooled reactor under development in Japan Atomic Energy Research Institute (JAERI). The dimensions, Young's modulus, tensile and bending strengths of specimens were measured before and after the irradiation creep test. Irradiation creep coefficients were obtained on the basis of the difference of dimensions of the unstressed and creeped specimens before and after the irradiation creep test. As a result, the irradiation creep coefficient was determined to be 3.4 × 10−29 −4.8 × 10−29 (MPa· nm2)−1 at 756–984°C up to 1.8 × 1025nm2 (E > 29 fJ). The average value was (4.22 ± 0.65) ×10−29 (MPa· nm2)−1, provided that the difference in irradiation temperature is neglected. Young's modulus increased 38–48% after irradiation. The increase in tensile strength of irradiation creeped specimen was 23–45% smaller than the bending strength. This suggests that the applied stress to the creep specimens under neutron irradiation gives rise to recovery of irradiation damage, compared with the case of unstressed specimens. The relation between the Young'a modulus ratio (E/E0) and the bending strength ratio (σb/σ0) can be expressed by the equation: σb/σo = (EE0)z, where z is a constant.