HTGR Knowledge Base

Conference Article: Notch sensitivity of graphite materials for VHTR

Kawakami, Haruo (Fuji Electric Corp. Research and Development Ltd., Yokosuka, Kanagawa (Japan))

Abstract

Most components in the core of a HTGR are made of graphite materials. These materials are efficient neutron moderators, and have high strength at high temperature, accordingly these have been used as nuclear materials long since. But the fracture mechanism of these materials is very peculiar, and has not been fully understood. Notch sensitivity is one of the most important properties in the design of the core structure. The experimental data on IG-11 and PGX have been scarcely reported, though these are the promising materials for the experimental VHTR is Japan. The authors investigated into the notch sensitivity of these materials by uniaxial tensile test, compressive test and thermal shock test by water quenching. The test materials were IG-11, SP2020 and PGX. The experimental method and the results are reported. The notch sensitivity of graphite materials in uniaxial tensile test became smaller as notch radius became smaller. The notch sensitivity of IG-11 was larger than that of PGX. The compressive fracture of PGX was of shear mode, while that of IG-11 was of the mixed mode of shear and transverse split. The thermal shock fracture resistance (TSFR) parameter of IG-11 was larger than that of PGX. But when a notch of a small radius existed, the TSFR of IG-11 was sometimes smaller than that of PGX.

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key words: compression strength; fracture properties; graphite; htgr type reactors; mechanical tests; notches; quenching; reactor components; reactor materials; sensitivity; stress intensity factors; tensile properties; thermal cycling; thermal shock; thermal stresses; carbon; gas cooled reactors; graphite moderated reactors; heat treatments; materials testing; mechanical properties
Reference:
Specialists' meeting on graphite component structural design, JAERI Tokai (Japan), September 8-11, 1986
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--11, pp:163-168