Radiation Effect Study on Tokai Carbon Nuclear Grade Graphite

TOKAI CARBON CO., LTD.Global Leader of Carbon Materials

Radiation Effect Study on Tokai Carbon Nuclear Grade Graphite

M. Fechter and Y. KatohOak Ridge National LaboratoryK. Takizawa and A. KondoTokai CarbonPresented at the 14th International Nuclear Graphite Specialists Meeting (INGSM-14)September 16-18, 2013, Seattle, Washington

DisclaimerAll data included in this presentation are

preliminary and are subject to revision after further analysis and certification processes are complete.

TOKAI CARBON CO., LTD.Global Leader of Carbon Materials

Materials for evaluation Nuclear grade graphite G347A and G458A manufactured by Tokai Carbon are used

for microstructural analysisG347A and G458A are both fine-grained isotropic graphite which have the advantage of being highly strength

G347A G458A

100μm 100μm

GradeBulk

density(g/cm3)

Electrical resistivity(µΩ̜•m)

Flexural strength(Mpa)

Coefficient of thermal expansion

(x10-6/℃)

Thermal conductivity(W/m ・ k)

Young’s modulus

(GPa)

G347A 1.85 11.0 49.0 4.2* (5.5**) 116 10.8

G458A 1.86 9.5 53.9 3.1* (4.4**) 139 11.3

* RT~100℃** RT~1000℃

Reference value

Takizawa et al., ICACC-2012

3 Managed by UT-Battellefor the U.S. Department of EnergyTOKAI CARBON CO., LTD.

Global Leader of Carbon Materials

Irradiation Matrix and Progress• Up to 4 x 1026 n/m2

at 300 – 900°C• Evaluation items

– Dimensional evolution– Thermal conductivity– Thermal expansivity– Elastic constants– Electrical resistivity– Flexural strength– Microstructures

0 10 20 30 40 500

300

600

900

1200

Fluence x1025 n/m2

Tem

pert

ure

ºC



Multi-Purpose Rabbit Approach1 2

XY

Z

X

Y

Z

813.248821.713

830.179838.644

847.109855.575

864.04872.506

880.971889.436

813.248821.713

830.179838.644

847.109855.575

864.04872.506

880.971889.436

ANSYS 12.0.1 ANSYS 12.0.1 • One rabbit for one irradiation condition.

• Custom-designed “mixed residence” capsule accommodates specimens of various types in a small rabbit vehicle.

• Irradiation temperatures are estimated for individual specimens based on thermal analysis (shown) and measurement of SiC temperature calibration specimens.



Dimensional Evolutions: Volume Changes

• Volume changes are plotted against fluence for nominal irradiation temperatures.

• Actual irradiation temperatures may be significantly off from the nominal irradiation temperatures.



Dimensional Evolutions: G347A Replotted for Estimated Irradiation Temperatures

• Volume changes are plotted for all specimen types.

• Plotted against estimated actual irradiation temperature.– Note that irradiation

temperature analysis is still in progress.

• Key trends are clearly shown. At the highest fluences here, – T < ~450°C: near the bottom

of submergence– T = ~600°C: irradiation strain

regressing to zero– T > ~750°C: already in

swelling regime



Dimensional Evolutions: G347A Replotted for Estimated Irradiation Temperatures

• Volume changes are plotted for all specimen types.

• Key trends are clearly shown. At the highest fluences here, – T < ~450°C: near the

bottom of submergence

– T = ~600°C: irradiation strain regressing to zero

– T > ~750°C: already in swelling regime



Dimensional Evolutions: G347A vs. G458A

• Data from side-by-side irradiation showing clear trends at 750°C.

• Initial contraction rate about the same for two graphite grades.

• Maximum contraction, fluence at contraction maximum, and fluence at zero volume change regression G458A > G347A.



Dimensional Evolutions: G347A (An)Isotropy

• Length changes for beam specimens (considered most accurate and reliable) are plotted.

• Orientations– AG = against gravity

= ~ with grain– WG = with gravity

= ~ against grain • Anisotropy in irradiation

strain is not negligible.– Likely common for

“isotropic” graphite.



Dimensional Evolutions: Differential Irradiation Strains

• WG dimensions are nearly always greater than AG dimensions.

• Magnitude of differential strain increases with fluence approaching a few percent.



Dynamic Young’s Modulus

• Pristine Young’s modulus ~11 GPa.

• Up to ~3.7 times increase by irradiation.

• Consistent with dimensional evolutions.



Dynamic Young’s Modulus

• Pristine Young’s modulus ~11 GPa.

• Up to ~3.7 times increase by irradiation.

• Consistent with dimensional evolutions. Elastic modulus peaks after maximum contraction occurs



Dynamic Young’s Modulus (2)• Pristine Young’s

modulus – G347A

• ~10.7 GPa (AG)• ~10.8 GPa (WG)

– G458A• ~12 GPa (WG)

• Young’s modulus appears isotropic after irradiation.

• Similar increase for two materials.



Equibiaxial Flexural Strength

• Trends consistent with evolutions of dimensions and Young’s modulus.

• Up to ~1.8 times increase in flexural strength may be explained by ~3.7 times increase in Young’s modulus.



Equibiaxial Flexural Strength

• Trends consistent with evolutions of dimensions and Young’s modulus.

• Up to ~1.8 times increase in flexural strength may be explained by ~3.7 times increase in Young’s modulus.

• Strength regression to pre-irradiation value when swelling approaches ~5%.



Mean Coefficient of Thermal Expansion

• Irradiation in general increased CTE.

• Greater increase in CTE at lower irradiation temperature. Diminishing irradiation effect as irradiation temperature approaches ~700°C.

• Defect annealing effect is apparent as temperature exceeds irradiation temperature.



Thermal conductivity

• Weak temperature dependence of irradiated thermal conductivity is noted.



Electric Resistivity

• Trend of electrical resistivity change may be characterized by a rapid increase followed by prolonged plateau.

• ~2.5 times increase appears consistent with IG-110 data by Ishiyama et al. (1996)



Discussion: Isotropic Irradiation EffectUnirr. Irrad.

CTE (RT-500C) WG/AG = 1.04 WG/AG = 1.04

ER WG/AG = 1.05 n/a

DYM WG/AG = 0.98 WG/AG = 0.98

TC (100-1000C) WG/AG = 1.00 n/a

Irrad. Strain - Significant

Collective Analysis of Microscopic Anisotropy?

Ratio of reflection Intensitylow high

Angle of maximum intensity

G347A

• Aspect ratios and orientation distributions for pores and filler particles: digital microscopy

• Crystallographic orientation distributions for fillers and matrix: ORNL MGEM-2 ellipsometric microscopy

0° 180°



Concluding Remarks• Irradiated properties data for Tokai Carbon nuclear grade graphites were

presented.– 2nd of 3 PIE campaigns in progress– Highest fluence at 2.7x1026 n/m2 fast (~20 dpa)

• Materials so far exhibit decent baseline properties after irradiation.– G347A appears promising for high radiation services – G458A may offer advantage in service life at high temperatures

• Anisotropy in irradiation response for “isotropic” graphite needs attention. • Future work

– More data coming from 2nd PIE campaign– Final PIE campaign anticipated to start in spring 2014– Microscopical analyses: unirradiated and irradiated





Technical Progress Summary

• Pre-irradiation studies– Draft report under final review

• Irradiation program– Progress approximately on schedule

• Post-irradiation examination– Campaign 1 complete– Campaign 2 in progress, on schedule– Data appear reasonable (following expected trend)

and promising

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Future Outlook

• PIE Campaign 2– Experimental work will complete soon– Further data analysis to follow

• PIE Campaign 3– After HFIR Operating Cycle 453, expected to start

in spring 2014– Conclusion of technical program anticipated in

2015

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Radiation Effect Study on Tokai Carbon Nuclear Grade Graphite