A unified model for strength degradation of oxidized IG-430 graphite column in VHTR

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Air-ingress events caused by large pipe breaks are important accidents considered in the safety analysis of Very High-Temperature Reactors (VHTRs). A main safety concern is the possibility of core-collapse following the failure of the graphite support column, which can be oxidized by ingressed air. The strength of the oxidized cylindrical graphite specimens under compressive load was tested using IG-430 graphite, a candidate material for the support structure of VHTR concept. The temperature conditions were 600 degrees C where the reaction rate is limited by the kinetics (Zone 1) and 800 degrees C where the reaction rate is affected by both kinetics and mass transfer rate (Zone 2). The graphite specimens were oxidized up to similar to 32% of total burn-off. In this study we suggest a new parameter for the unified strength degradation model. The derived Knudsen relation with corrected burn-off in this study is applicable to predict the strength degradation of a graphite column that oxidized in Zone 1 and Zone 2. The exponent k in the Knudsen relation was empirically obtained as 0.079. The obtained relation is applicable to a maximum corrected burn-off of 22%. The Zone 3 is surface oxidation. The strength degradation of graphite column oxidized in Zone 3 can be evaluated by developing the empirical straight line formula. This combination of the empirical straight line formula and the Knudsen relation in terms of corrected burn-off enables us to predict the strength degradation of a graphite column oxidized in Zones 1, 2 and 3. (C) 2012 Elsevier B.V. All rights reserved.
Publisher
ELSEVIER SCIENCE BV
Issue Date
2012-05
Language
English
Article Type
Article
Keywords

OXIDATION

Citation

JOURNAL OF NUCLEAR MATERIALS, v.424, no.1-3, pp.132 - 137

ISSN
0022-3115
DOI
10.1016/j.jnucmat.2012.02.009
URI
http://hdl.handle.net/10203/103876
Appears in Collection
NE-Journal Papers(저널논문)
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