Evaluation of oxidation characteristics of fine-grained graphites (IG-110 and IG-430) for very high temperature reactor; Changes in density distribution and compressive strength caused by air-oxidation

Fujita, Ichiro*; Eto, Motokuni*; Osaki, Hirotaka; Shibata, Taiju ; Sumita, Junya ; Konishi, Takashi; Yamaji, Masatoshi; Kunimoto, Eiji

Graphite components in HTGR and VHTR may be oxidized by impurities in coolant helium-gas even at normal operation, as well as by air at air-ingress accident. In this study, by air-oxidation test at 520-900C, oxidation characteristics of IG-110 and IG-430 graphites, and associated decrease in compressive strength were examined. The following results were obtained. (1) The activation energy of the air-oxidation for IG-430 is 176 kJ/mol being almost same as for IG-110, though the oxidation rate for IG-430 is less than a half of that for IG-110. (2) There are correlations between density change and decrease in compressive strength. Decrease in strength is the largest in case that the oxidation temperature is lower than 600 C where the homogenous oxidation occurs. (3) In the process of oxidation, amorphous binder regions are predominantly oxidized. It suggests that peeling-off of cokes grains is necessary to be considered for oxidation weight loss, as well as gasification.