Penetration depth and transient oxidation of graphite by oxygen and water vapor

Wichner, R.P.; Burchell, Timothy D; Contescu, Cristian I.

doi:10.1016/j.jnucmat.2009.06.032

Cited by 33 publications

(23 citation statements)

References 6 publications

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“…Although on different grades of nuclear graphite, the results reported here for PCEA graphite correlate well with previous observations from the ORNL group [10] on development of non-uniform density profiles in oxidized specialty grade graphite (R4-650). The results are also in very good agreement with recent theoretical estimates advanced by ORNL researchers [13,14] on penetration depth of the oxidant gas at quasi-steady state oxidation conditions. These results confirm one more time the validity of the chemically reactive oxidation zone proposed by Wichner and Ball (ORNL) [17].…”

Section: Discussion: Oxidation Effects On Mechanical Strengthsupporting

confidence: 88%

“…A short letter containing the results has been very recently accepted for publication [14]. Although based on several simplifying approximations, the analytical method predicts the development of non-uniform oxidation profiles by oxidation with water vapor or oxygen, their time evolution to a steady state condition, and the effect of temperature.…”

Section: Previous Results Of Graphite Oxidation Research At Ornlmentioning

confidence: 99%

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Characterization of Porosity Development in Oxidized Graphite using Automated Image Analysis Techniques

Contescu¹,

Burchell²

2009

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Section: Discussion: Oxidation Effects On Mechanical Strengthsupporting

confidence: 88%

Section: Previous Results Of Graphite Oxidation Research At Ornlmentioning

confidence: 99%

Characterization of Porosity Development in Oxidized Graphite using Automated Image Analysis Techniques

Contescu¹,

Burchell²

2009

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“…The activation energy for GKrS was determined to be 111.5 kJ/mol in the kinetic regime, from 873 to 1023 K. It is supposed that the lower activation energy of GKrS matrix graphite could be attributed to the preferential oxidation of the binder phase in the kinetic regime [10]. Many researchers have observed the preferential binder oxidation in their studies as well [11][12][13]. The preferential oxidation of binder often has a significant influence on the degradation of mechanical properties of graphite in the kinetic regime of graphite oxidation that may lead to severe consequences such as failure of pebble fuel elements and subsequent release of large amounts of radioactive fission products.…”

Section: Science and Technology Of Nuclear Installationsmentioning

confidence: 99%

Oxidation Behavior of Matrix Graphite and Its Effect on Compressive Strength

Zhou

Contescu

Zhao

et al. 2017

Science and Technology of Nuclear Installations

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Matrix graphite (MG) with incompletely graphitized binder used in high-temperature gas-cooled reactors (HTGRs) is commonly suspected to exhibit lower oxidation resistance in air. In order to reveal the oxidation performance, the oxidation behavior of newly developed A3-3 MG at the temperature range from 500 to 950 ∘ C in air was studied and the effect of oxidation on the compressive strength of oxidized MG specimens was characterized. Results show that temperature has a significant influence on the oxidation behavior of MG. The transition temperature between Regimes I and II is ∼700 ∘ C and the activation energy ( ) in Regime I is around 185 kJ/mol, a little lower than that of nuclear graphite, which indicates MG is more vulnerable to oxidation. Oxidation at 550 ∘ C causes more damage to compressive strength of MG than oxidation at 900 ∘ C. Comparing with the strength of pristine MG specimens, the rate of compressive strength loss is 77.3% after oxidation at 550 ∘ C and only 12.5% for oxidation at 900 ∘ C. Microstructure images of SEM and porosity measurement by Mercury Porosimetry indicate that the significant compressive strength loss of MG oxidized at 550 ∘ C may be attributed to both the uniform pore formation throughout the bulk and the preferential oxidation of the binder.

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“…He concluded that gasification of graphite elements will be confined at the coolant-graphite interface, and therefore corrosion by steam should not affect normal operation of HTGR, provided steam concentration is kept below 0.01 Pa. This conclusion was reiterated by more recent estimates, all based on the same graphite-specific parameters reported by GA for reaction of H-451 grade with water [12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 97%

Oxidation of PCEA nuclear graphite by low water concentrations in helium

Contescu¹,

Mee²,

Wang³

et al. 2014

Journal of Nuclear Materials

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a b s t r a c tAccelerated oxidation tests were performed to determine kinetic parameters of the chronic oxidation reaction (i.e. slow, continuous, and persistent) of PCEA graphite in contact with helium coolant containing low moisture concentrations in high temperature gas-cooled reactors. To the authors' knowledge such a study has not been done since the detailed analysis of reaction of H-451 graphite with steam (Velasquez, Hightower, Burnette, 1978). Since that H-451 graphite is now unavailable, it is urgently needed to characterize chronic oxidation behavior of new graphite grades that are being considered for use in gas-cooled reactors. The Langmuir-Hinshelwood mechanism of carbon oxidation by water results in a non-linear reaction rate expression, with at least six different parameters. They were determined in accelerated oxidation experiments that covered a large range of temperatures (800-1100°C), and partial pressures of water (15-850 Pa) and hydrogen (30-150 Pa) and used graphite specimens thin enough (4 mm) in order to avoid diffusion effects. Data analysis employed a statistical method based on multiple likelihood estimation of parameters and simultaneous fitting of non-linear equations. The results show significant material-specific differences between graphite grades PCEA and H-451 which were attributed to microstructural dissimilarity between the two materials. It is concluded that kinetic data cannot be transferred from one graphite grade to another.

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Penetration depth and transient oxidation of graphite by oxygen and water vapor

Cited by 33 publications

References 6 publications

Characterization of Porosity Development in Oxidized Graphite using Automated Image Analysis Techniques

Characterization of Porosity Development in Oxidized Graphite using Automated Image Analysis Techniques

Oxidation Behavior of Matrix Graphite and Its Effect on Compressive Strength

Oxidation of PCEA nuclear graphite by low water concentrations in helium

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