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Conference Article: A graphite corrosion rate equation under high concentration water-vapor in helium and an estimation of the VHTR support post corrosion and strength

Nomura, S.; Kurosawa, T.; Imai, H.; Eto, M.; Oku, T. (Japan Atomic Energy Research Inst., Tokai, Ibaraki. Tokai Research Establishment)

Abstract

To estimate corrosion of a candidate graphite material IG-110 in the very high temperature gas-cooled reactor, a rate equation for oxidation with water-vapor in-pore diffusion control regime was derived applying Langmuir-Hinshelwood mechanism as contribution of chemical rate for the over all oxidation rate. On the basis of the equation, the corrosion behaviors of the core support post graphite material were studied by using various dependence of the chemical rate on water-vapor concentration and by using laboratory data obtained in the oxidation of IG-110 graphite specimen with water-vapor of 6.5 x 10-3 atm in helium stream at atmospheric pressure. The corrosion rate, weight loss with time was calculated for core support post graphite under water ingress accident of the reactor. Results calculated based on the equation were compared with those calculated by another equation, in which the chemical rate is assumed to be directly proportional to the concentration of water-vapor. It was found that the former gives the weight loss approximately one order of magnitude smaller than the latter in the case of water ingress accident. The results obtained by the equation using Langmuir-Hinshelwood mechanism are considered to be more reliable. The time needed to reach steady state concentration profile of water vapor in the core support post graphite was also evaluated. Local burn-off profiles across the post were figured based on the steady state concentration profile of water-vapor in it. The changes in compressive strength brought by the corrosion in accident were also estimated.

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key words: corrosion; graphite; helium; htgr type reactors; isotropy; medium pressure; numerical solution; reactor cores; supports; time dependence; water vapor; carbon; chemical reactions; gas cooled reactors; graphite moderated reactors; mechanical structures; reactor components
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:195-200