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Detailed oxidation mechanism
of nuclear graphite
Yao WANG , Suyuan YU04/21/23
Institute of Nuclear and New Energy Technology
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Hundreds of tones of graphite in HTGR
Moderator, reflector and structure material
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Graphite oxidation in HTGR
Reaction1/2O2+C=CO
O2+C=CO2
1/2O2+CO+CO2
C+H2O=CO+H2
C+2H2O=CO2+2H2
C+CO2=2CO
C+2H2=CH4
CO+H2O=CO2+H2
H2O, O2, CO2, CO, H2,
…
Refueling
Maintenance
Outgassing
leakage
The oxidation-induced strength loss of nuclear graphite is one of the most important issues for HTGR design. 22 yCOxCOzOC
Consider oxygen oxidaiton only
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Experimental Study of the Kinetics
thermogravimetry analysis
Muffle furnace
Gas analysis
exp( )g
EaR A
R T
Parameters in Arrhenius equation:
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Global Kinetics from experiments
NO. Graphite Ea(kJ/mol) n T(K) Method
1 IG-110 186.96 1 673~ TGA
2 IG-11 158.56 1 673~873 TGA
3 IG-110 218 0.75 813~903 Gas analysis
4 IG-430 158.5 0.37 813~1073 Gas analysis
5 NBG 167.35 0.5 800 ~1050 TGA
6 pure Graphite
188.37 0 1000~1300 TGA
7 SP-1 204 0.83~0.51 733~842 Gas analysis
1.Wichner R P, Burchell T D, Contescu C I. Penetration depth and transient oxidation of graphite by oxygen and water vapor. J Nucl Mater, 2009, 393(3):518-521.2. Luo X W, Robin J C, Yu S Y. Effect of temperature on graphite oxidation behavior. Nucl Eng Des, 2004, 227(3):273-280.3. Kim E S, No H C. Experimental study on the oxidation of nuclear graphite and development of an oxidation model. J Nucl Mater, 2006, 349(1-2):182-194.4. Oh C H, Kim E S, NO H C, et al. Final report on experimental validation of stratified flow phenomena, graphite oxidation, and mitigation strategies of air ingress accidents. Idaho Falls, USA: Idaho National Laboratory, 2011. INL/EXT-10-20759.5. Gelbard F. Graphite oxidation modeling for application in melcor. Livermore, USA: Sandia National Laboratories, 2009. SAND2008-7852.6. Froberg R. W. and R. Essenhigh, “Reaction Order and Activation Energy of Carbon Oxidation During Internal Burning,” 17th Symposium (International) on Combustion, Pittsburgh, PA, pp. 179-187, 1978.7. Ranish, J. M., and Walker, P. L. Jr., Carbon 31:135 (1993).
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[1]IG-110
PCEA
NBG-18
[1] Peng WANG, et. al.
Motivation for detailed oxidation(1)
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Motivation for detailed oxidation(2)
CO2,H2O
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Graphite surface site types
zig-zag
arm chair
arm chair
zig
-zag
uncomplete arm chair
zig-zag
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[1]
Density functional study( zig-zag site)
[1] Karina Sendt, Brian S. Haynes
[1]
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Density functional study(arm-chair site)
[1] Karina Sendt, Brian S. Haynes
[1]
O2 chemisorption: +O2 → → → Ⅰ Ⅱ Ⅲ Ⅳ CO desorption: → + CO → +2 COⅣ Ⅴ Ⅵ
Oxide rearrangement: → → + COⅣ Ⅶ Ⅴ
[1]
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Graph Theory
1
2
3
5 47
8
18
CO
6
CO
17 15 11 9
101216 CO CO
O2
19 O
k+1
-7.52
k-1
459
k+2
-1.15k-2
278
k+7
156k-7
47
k+8
61k-8
217
k+20
-6
k-20
137
k+21
144
k-21
14
k+3
428k-3
294
k-4
72
k+4
352
k+9
354
k-9
91
k+5
-0.76
k-5
169
k-6
341k+6
34.5 k-11
138
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14
k+11
179
k+12
242
k-12
5.2 k+10
167k-10
11.2
The Seven Bridges of Königsberg
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Under normal operation conditions, the Quasi-steady state assumption is available:
Quasi-Steady State assumption
(s)0
Ci
t
2K(1)[O ]*C(1)=C(2)
K(2)*C(2)=C(3)
K(3)*C(3)=C(4)
k(4)*C(4)-k(17)*C(5)*[CO]=-(k(6)*C(4)-k(19)*C(7))
k(6)*C(4)-k(19)*C(7)=k(7)*C(7)-k(20)*C(5)*[CO]
[k(4)+k(6)]*C(4)=k(19)*C(7)+k(17)[CO]*C(5)
k(6)*C(4) [k(7)+
0
k(19)]*C(7)-k(20)[CO]*C(5)
k(4)+k(6) k(19)*C(7)+k(17)[CO]*C(5)
k(6) [k(7)+k(19)]*C(7)-k(20)[CO]*C(5)
C(1) C(2) C(3) C(4) C(5) C(7)
k(6)*C(4)=k(19)*C(7)
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Prelimilary results
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Apply the detailed oxidation model to diferrent graphite surface types to make a complete surface model for the pure graphite;
Consider the graphite impurities' influences to the oxidation behavior, such as catalytical effect of metals in graphite;
Couple the detailed surface model with pore development during oxidaiton for the more accurate simulation.
Future work
Thank you!
Yao WANG04/21/23