Pre-irradiation And Specimen Size Effect Study of Nuclear Grade Graphite IGS743NH

1. Pre-irradiation And Specimen Size Effect Study of Nuclear Grade Graphite IGS743NH INGSM-14 September 15-18, 2012 M. Snead (Fechter)1, Y. Katoh1, N. Cetiner1, T. Muto2, R. Yamashita2, Y. Mitarai3 1 Oak Ridge National Laboratory 2Nippon Techno-Carbon 3 Nippon Steel & Sumikin Chemical

2. Contents • Program overview • Material and properties to be investigated • Irradiation matrix: fluence and temperature • Rabbit design • Schedule • ORNL sample size and pre-irradiation program results • Specific gravity • CTE • Thermal conductivity (diffusivity) • Dynamic Young’s and shear moduli • Electrical resistivity • Strength

3. Material and Properties to be Investigated • NTC Graphite Grade IGS-743NH • Iso-molded • Super-fine grained • Properties to be examined for irradiation effects • Dimensional change • Coefficient of thermal expansion • Thermal conductivity • Electrical resistivity • Dynamic Young’s and shear moduli • Flexural Strength • Tensile strength

4. Matrix of Irradiation Conditions ~1200ºC ~1000ºC Prismatic Core Temperature Pebble-bed Core ~600ºC ~300ºC 10 20 30 40 Fast Fluence, x1025 n/m2

5. Fluence and Temperature in Estimated Irradiation Strain Trend 1 1Not included in program

6. Irradiation in HFIR Target Rabbit Facility • Use of HFIR “rabbit” vehicles allows irradiation of individual tiny capsules at desired temperatures to desired fast neutron fluences. • Fast flux ~1x1019 n/m2/s, or ~2.1x1025 n/m2 (~1.5 dpa in graphite) during 24-day operating cycle for HFIR. • Irradiation temperatures 300 to 1300ºC in recent programs.

7. Rabbits Design: CTE Beam (CB) and Modulus Beam (MB) Configurations 57.2 mm 57.2 mm

8. Rabbit Design: Tensile Configuration – a Challenge • Limited interior volume in a rabbit capsule • Maximum specimen diameter ~6 mm • Epoxy-extension essential • Graphite of interest is of high strength • ~35 MPa tensile unirradiated; irradiated strength may be higher • Will require a reduced diameter gauge section • Miniature tensile specimen geometry is newly developed • 25 mm total length, 6 mm diameter at glued ends • Gauge dimensions Ø 4 mm x L14 mm (L/Ø = 3.5) • Validation study is required Metallic Connector Specimen Epoxy Glue here

9. Rabbit Design: Tensile Configuration ~50 mm

10. Irradiation Program Prospect • Planning schedule as of September 2013 • First rabbits start irradiation on November 19th, 2013 • First rabbits will be shipped for post irradiation examination (PIE) in May 2014 • Second shipment of rabbits will be February 2015 • Third and last shipment of rabbits will be July 2016 • This is all dependent on the HFIR operation that could change. Currently it is assumed that HFIR operates 6 cycles a year.

11. ORNL Pre-Irradiation Evaluation Program:Test Methods

12. Definition of Orientations for Iso-molded Graphite Z = (against grain) = with gravity = axial (Ax) X = (with grain) = against gravity = transverse (Tr) Y = (with grain) = against gravity = transverse (Tr)

13. ORNL Pre-Irradiation Evaluation Program:Specific Gravity

14. Room Temperature Thermal Conductivity Ax: axial orientation; Tr: transversal orientation;Numbers in parentheses are one standard deviations. Ø10 x 2 mm Ø8 x 2 mm Ø6 x 2 mm

15. Thermal Conductivity Error bars equal ±1 standard deviations • Insignificant effect of specimen diameter or thickness. • Insignificant difference between two orientations.

16. Coefficient of Linear Thermal Expansion CTE Anisotropy Ratio @ 500ºC = ~1.1 Error bars equals 1 standard deviation

17. Dynamic Young’s and Shear Moduli Isotropy ratio = ~1.1 Type MB specimen Type CB specimen

18. Electrical Resistivity Isotropy ratio = ~1.1

19. Flexural Strength - Equibiaxial strength Specimen type 3SQ6

20. Flexural Strength - Equibiaxial strength • Views are from tensile surface of the specimens. • Concentric circles indicate approximate locations of contact with the support and loading rings. • Failure origination from random locations within the loading ring circle indicates sufficiently uniform stress distribution until the initial cracking.

21. Tensile Strength: Specimen Size Effect Validation

22. TS4 with Steel Extenders and Alignment Block Setup Alignment block top Steel extensor V notch Push screw Alignment block base

23. Tensile Strength – Preliminary Results TS6.5U Axial Specimen X-Y Strain Gauge Reading Poisson’s ratio: 0.13 Unibody Specimens • No significant effects of gauge diameter and epoxy-extension. • More discussion in Katoh et al ASTM paper later this week. Epoxy-extended Specimens

24. Data Comparison for : IGS743NHNTC vs. ORNL Pre-Irradiation Evaluation • Reasonable agreement has been observed between data generated by NTC and ORNL

25. Summary • ORNL program for evaluation of NTC’s nuclear graphite was initiated and in progress. • Planned irradiation program will examine baseline physical, thermal, and mechanical properties after fast neutron irradiation up to ~3.2 x 1026 n/m2 at 400 – 1200 ºC. Irradiation vehicles have successfully been developed. • Pre-irradiation evaluation program is in progress. • All baseline properties are being positively addressed, including density homogeneity, thermal properties, and strength. • ORNL data are consistent with manufacturer-claimed properties. • Result from tensile specimen size effect study likely validate the use of small gauge diameter specimens.