TOKAI CARBON CO., LTD. Global Leader of Carbon Materials Radiation Effect Study on Tokai Carbon Nuclear Grade Graphite M. Fechter and Y. Katoh Oak Ridge National Laboratory K. Takizawa and A. Kondo Tokai Carbon Presented at the 14 th International Nuclear Graphite Specialists Meeting (INGSM-14) September 16-18, 2013, Seattle, Washington Disclaimer All 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 analysis G347A and G458A are both fine-grained isotropic graphite which have the advantage of being highly strength G347A G458A 100μm Grade Bulk density (g/cm 3 ) Electrical resistivity (µΩ ̜ m) Flexural strength (Mpa) Coefficient of thermal expansion (x10 -6 / ℃ ) Thermal conductivity (W/m ・ k) Young’s modulus (GPa) G347A * (5.5**) G458A * (4.4**) * RT~100 ℃ ** RT~1000 ℃ Reference value Takizawa et al., ICACC-2012

3Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials Irradiation Matrix and Progress Up to 4 x n/m 2 at 300 – 900°C Evaluation items – Dimensional evolution – Thermal conductivity – Thermal expansivity – Elastic constants – Electrical resistivity – Flexural strength – Microstructures

4Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials Multi-Purpose Rabbit Approach 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.

5Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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.

6Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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

7Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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

8Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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.

9Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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.

10Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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.

11Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials Dynamic Young’s Modulus Pristine Young’s modulus ~11 GPa. Up to ~3.7 times increase by irradiation. Consistent with dimensional evolutions.

12Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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

13Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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.

14Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon 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.

15Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon 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. Strength regression to pre- irradiation value when swelling approaches ~5%.

16Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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.

17Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials Thermal conductivity Weak temperature dependence of irradiated thermal conductivity is noted.

18Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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)

19Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials Discussion: Isotropic Irradiation Effect Unirr.Irrad. CTE (RT-500C)WG/AG = 1.04 ERWG/AG = 1.05n/a DYMWG/AG = 0.98 TC ( C)WG/AG = 1.00n/a Irrad. Strain-Significant

Collective Analysis of Microscopic Anisotropy? Ratio of reflection Intensity lowhigh 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°0°180°

21Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials Concluding Remarks Irradiated properties data for Tokai Carbon nuclear grade graphites were presented. – 2 nd of 3 PIE campaigns in progress – Highest fluence at 2.7x10 26 n/m 2 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 2 nd PIE campaign – Final PIE campaign anticipated to start in spring 2014 – Microscopical analyses: unirradiated and irradiated

22Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials

23Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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 Move to backup

24Managed by UT-Battelle for the U.S. Department of Energy TOKAI CARBON CO., LTD. Global Leader of Carbon Materials 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 Move to backup