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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[1]

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

13

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