Experimental study on the oxidation of nuclear graphite and development of an oxidation model

Kim, Eung Soo; No, Hee Cheon

doi:10.1016/j.jnucmat.2005.10.015

Cited by 73 publications

(31 citation statements)

References 5 publications

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“…The reason is not yet identified. In Kim et al(2006) and the current experiments, the maximum oxidation rate occurs at about 35% burn-off, at which time the oxidation rate is about 6.4 times that of the initial oxidation rate. Figure 4-17 (b) shows the data for H451 graphite.…”

Section: Graphite Oxidation Degree Vs Graphite Oxidation Ratesupporting

confidence: 46%

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FINAL REPORT on Experimental Validation of Stratified Flow Phenomena, Graphite Oxidation, and Mitigation Strategies of Air Ingress Accidents

Oh¹,

Kim²,

No³

et al. 2011

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(NGNP)/Generation IV very high temperature reactor (VHTR). Phenomena Identification and Ranking studies to date have identified the air ingress event, following on the heels of a VHTR depressurization, as being very important. Consequently, the development of advanced air ingress-related models and verification and validation are a very high priority for the NGNP Project.Following a loss of coolant and system depressurization incident, air ingress will occur through the break, leading to oxidation of the in-core graphite structure and fuel. This study indicates that depending on the location and the size of the pipe break, the air ingress phenomena are different. In an effort to estimate the proper safety margin, experimental data and tools, including accurate multidimensional thermal-hydraulic and reactor physics models, a burn-off model and a fracture model are required. It will also eventually require effective strategies to mitigate the effects of oxidation.This 3-year project (FY 2008 to FY 2010 focused on various issues related to the VHTR air-ingress accident, including (a) analytical and experimental study of air ingress caused by density-driven, stratified, countercurrent flow, (b) advanced graphite oxidation experiments, (c) experimental study of burn-off in the core bottom structures, (d) structural tests of the oxidized core bottom structures, (e) implementation of advanced models developed during the previous tasks into the GAMMA code, (f) full air ingress and oxidation mitigation analyses, (g) development of core neutronic models, (h) coupling of the core neutronic and thermal hydraulic models, and (i) verification and validation of the coupled models. E-1. RESEARCH OBJECTIVESThe main objectives of this 3-year project were to investigate air-ingress related phenomena in the VHTRs and perform modeling and experiments for better understanding on the accident consequences. The major phenomena, targeted in this study, were (1) density gradient driven stratified flow, (2) graphite oxidation and structural degradation, (3) thermal hydraulics and neutronics coupling, and (4) development of air ingress mitigation and computational fluid dynamics (CFD) calculations E-2. REPORT CONTENT AND ORGANIZATIONThis report, which highlights key accomplishments achieved from FY 2008 to FY 2010, consists of the following sections:1. Introduction: Section 1 is introductory information about this project with objectives and strategies.

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Section: Graphite Oxidation Degree Vs Graphite Oxidation Ratesupporting

confidence: 46%

“…This graph includes three datasets: , Kim et al (2006), and (3) the experimental results obtained in this work. According to the figure, the data from Kim et al (2006) and this work show very good agreement. However, the data from shows some discrepancies from other data.…”

Section: Graphite Oxidation Degree Vs Graphite Oxidation Ratementioning

confidence: 99%

FINAL REPORT on Experimental Validation of Stratified Flow Phenomena, Graphite Oxidation, and Mitigation Strategies of Air Ingress Accidents

Oh¹,

Kim²,

No³

et al. 2011

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“…The results for both materials are plotted together in Figure 7 by normalizing the PCEA to the higher initial NBG-18 strength, S0 = 88.39 MPa, and forcing the fitted PCEA lines through the appropriate y-intercept instead of through the origin. 7KH DYHUDJH LQLWLDO EXON JUDSKLWH GHQVLW\ ȡ FDOFXODWHG IURP PHDVXUHG VDPSOH PDVVHV LQ combination with height and diameter information) was 1.88 g/cm 3 for NBG-18, and 1.81 g/cm 3 for PCEA, close enough to yield a valid comparison. Given the slopes of the respective lines, some tentative conclusions can be drawn.…”

Section: Time (Hours)mentioning

confidence: 78%

Status of Graphite Oxidation Work

Smith¹

2010

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Data were developed to compare the extent of structural damage associated with high temperature exposure to an air leak. Two materials, NBG-18 graphite and unpurified PCEA graphite have been tested as of this report. The scope was limited to isothermal oxidation at a single temperature, 750°C. Ambient postoxidation compression strength testing was performed for three levels of burn off (1%, 5%, and 10% mass loss) for two leak scenarios: 100% air and 10% air in helium. Temperature, gas flow, and dynamic mass loss oxidation conditions were monitored and recorded for each sample. The oxidation period was controlled with flow of inert gas during the thermal ramp and upon cool down with a constant 10 liter per minute flow maintained throughout furnace operation. Compressive strengths of parallel un-oxidized samples were tested to assess the relative mass loss effects. In addition to baseline samples matching the unoxidized dimensions of the oxidized samples, two sets of mechanically reduced samples were prepared. One set was trimmed to achieve the desired mass loss by removing an effectively uniform depth from the geometric surface of the sample. The other set was cored to produce a full penetration axial hole down the center of each sample. vii viii ACKNOWLEDGEMENTS

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“…Determined activation energy for the tested waste graphite powder is a little smaller than the reported activation energies of IG-110 graphite, which are in the range of 187.9-218 kJÁmol À1 . 8,9) This difference can be explained by the difference in the sample size and the surface area of the tested graphite sample. As the oxidation reactions take place on the graphite surface, the smaller graphite samples tended to react faster than the larger graphite samples due to their higher surface area/ mass ratio.…”

Section: Resultsmentioning

confidence: 99%

Analysis of Combustion Kinetics of Powdered Nuclear Graphite by using a Non-isothermal Thermogravimetric Method

Yang

Eun

Lee

et al. 2006

Journal of Nuclear Science and Technology

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Experimental study on the oxidation of nuclear graphite and development of an oxidation model

Cited by 73 publications

References 5 publications

FINAL REPORT on Experimental Validation of Stratified Flow Phenomena, Graphite Oxidation, and Mitigation Strategies of Air Ingress Accidents

FINAL REPORT on Experimental Validation of Stratified Flow Phenomena, Graphite Oxidation, and Mitigation Strategies of Air Ingress Accidents

Status of Graphite Oxidation Work

Analysis of Combustion Kinetics of Powdered Nuclear Graphite by using a Non-isothermal Thermogravimetric Method

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