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Conference Article: Effect of atmosphere on the bend strength of nuclear graphite

Maruyama, T. (Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center)

Abstract

Investigations were made of the effects of test environments on bend strength and fracture toughness of fine-grained isotropic graphites. Four-point bend tests were carried out in various atmospheres of air, helium and vacuum. When room temperature bend tests were carried out for specimens which had been outgassed in vacuum at high temperature, we obtained higher values than those measured in air by up to 45%. When measurements were made in helium atmosphere containing 1 to 3 ppm of water vapor, bend strength was higher by 20 to 30% than those measured in air. When water content in helium increased to about 20 ppm, the strength became the same with that measured in air. The high temperature bend strength of graphite specimens generally increased with increasing temperature up to 1200 deg. C if it had not been outgassed at 1200 deg. C. Whereas, the bend strength of specimens which had been outgassed at 1200 deg. C showed high room temperature strength followed by negative temperature dependence up to 900 deg. C, and then became temperature independent up to 1200 deg. C. The fracture toughness of fully outgassed specimens measured in vacuum had higher values by about 20% than that measured in air.

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key words: controlled atmospheres; fracture properties; graphite; helium; high vacuum; materials testing; mechanical tests; temperature dependence; tensile properties; water vapor; carbon
Reference:
Specialists' meeting on the status of graphite development for gas cooled reactors. Tokai, Ibaraki (Japan). 9-12 Sep 1991
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--690, pp:177-182