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
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
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
Matrix of Irradiation Conditions ~1200ºC ~1000ºC Prismatic Core Temperature Pebble-bed Core ~600ºC ~300ºC 10 20 30 40 Fast Fluence, x1025 n/m2
Fluence and Temperature in Estimated Irradiation Strain Trend 1 1Not included in program
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.
Rabbits Design: CTE Beam (CB) and Modulus Beam (MB) Configurations 57.2 mm 57.2 mm
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
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.
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)
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
Thermal Conductivity Error bars equal ±1 standard deviations • Insignificant effect of specimen diameter or thickness. • Insignificant difference between two orientations.
Coefficient of Linear Thermal Expansion CTE Anisotropy Ratio @ 500ºC = ~1.1 Error bars equals 1 standard deviation
Dynamic Young’s and Shear Moduli Isotropy ratio = ~1.1 Type MB specimen Type CB specimen
Electrical Resistivity Isotropy ratio = ~1.1
Flexural Strength - Equibiaxial strength Specimen type 3SQ6
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.
TS4 with Steel Extenders and Alignment Block Setup Alignment block top Steel extensor V notch Push screw Alignment block base
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
Data Comparison for : IGS743NHNTC vs. ORNL Pre-Irradiation Evaluation • Reasonable agreement has been observed between data generated by NTC and ORNL
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.