INGSM-14 Seattle, USA, 15-18 September 2013

Nippon Techno Carbon Co, LtdNippon Steel & Sumikin Chemical

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

INGSM-14 September 15-18, 2012M. Snead (Fechter)1, Y. Katoh1, N. Cetiner1,T. Muto2, R. Yamashita2, Y. Mitarai3

1 Oak Ridge National Laboratory2 Nippon Techno-Carbon 3 Nippon Steel & Sumikin Chemical

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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

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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

Property Unit IGS-743Catalog

Grain size mm <0.05

Density g/cm3 1.80

Flexural Strength MPa 54

Tensile Strength MPa 35

Thermal Conductivity W/m-K 128

CTE (RT-500°C) ppmK-1 4.8

Resistivity Ω-m 12.5

Standard Billet Size mm 350 x 630 x 1020

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Matrix of Irradiation Conditions

Tem

per

atu

re

Fast Fluence, x1025 n/m2

~600ºC

~300ºC

~1000ºC

10

~1200ºC

Prismatic Core

20 30 40

Pebble-bed Core

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Fluence and Temperature in Estimated Irradiation Strain Trend

1Not included in program

1

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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.

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Rabbits Design: CTE Beam (CB) and Modulus Beam (MB) Configurations

57.2 mm

57.2 mm

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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

SpecimenMetallic Connector Epoxy Glue here

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Rabbit Design: Tensile Configuration

~50 mm

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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.

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ORNL Pre-Irradiation Evaluation Program:Test Methods

Property MethodASTM

Standard (Graphite)

ASTM Standard

(Ceramics)

Specimen Type

Specimen Dimensions

(mm)

DensityDimensional

inspection and mass

C559 Rectangular Beam

24x3.5x2.25 Etc.

Elastic constants

Sonic resonance C747 C1259 Rectangular

Plate/Beam24x3.5x2.2548x6.0x1.0

CTE Push rod E228 E228 Bar 24x3.5x2.25

Thermal diffusivity Laser flash E1461 E1461 Disc

Ø6 x 1/2/3Ø8 x 2Ø10 x2

Flexural strength Equibiaxial N/A C1499 Coupon 6 x 6 x 0.5

Tensile strength N/a Tensile rod

Gauge dim. Ø6.5 x 26

Ø4 x 14 etc.

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Definition of Orientations for Iso-molded Graphite

X = (with grain) = against gravity = transverse (Tr)

Y = (with grain) = against gravity = transverse (Tr)

Z = (against grain) = with gravity = axial (Ax)

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ORNL Pre-Irradiation Evaluation Program:Specific Gravity

Specimen Type Dimensions No. of

SpecimensAverage (g/cm3)

Std.Dev. (g/cm3) Remarks

CB 24x3.5x2.25 124 1.791 0.006

MB 48x6.0x1.0 64 1.785 0.005

TD6-1 Ø6x1 8 1.788 0.006

TD6-2 Ø6x2 90 1.799 0.007

TD6-3 Ø6x3 8 1.797 0.005

TD8-2 Ø8x2 8 1.794 0.005

TD10-2 Ø10x2 8 1.801 0.004

3SQ6 18x6x0.5 72 1.794 0.008

Tensile various Only gauge diameter and length measured

All 382 1.793 0.008

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Room Temperature Thermal Conductivity

Ax: axial orientation; Tr: transversal orientation;Numbers in parentheses are one standard deviations.

Spec. Type DimensionsThermal

(mm2

Ax.

Diffusivity/ s)

Tr.

Thermal(W /

Ax.

Conductivitym-K)

Tr.TD6-1 Ø6x1 89.7 (1.2) 117.6 (1.6)

TD6-2 Ø6x2 88.4 (0.6) 95.4 (2.5) 116.3 (0.9) 126.2 (3.3)

TD6-3 Ø6x3 86.5 (0.8) 113.9 (1.4)

TD8-2 Ø8x2 89.4 (0.9) 117.6 (1.3)

TD10-2 Ø10x2 87.0 (0.2) 114.9 (0.3)

All 116.2 (1.9) 126.2 (3.3)

Ø10 x 2 mm

Ø8 x 2 mmØ6 x 2 mm

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Thermal ConductivityError bars equal ±1 standard deviations

• Insignificant effect of specimen diameter or thickness.

• Insignificant difference between two orientations.

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Coefficient of Linear Thermal Expansion

Error bars equals 1 standard deviation

CTE Anisotropy Ratio @ 500ºC = ~1.1

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Dynamic Young’s and Shear Moduli

Spec.Type

Dimensions(X x Y x Z)

mmOrient No. of

Tests

Young’sMod.GPa

( Std.Dev. )

ShearMod.GPa

( Std.Dev. ) Poisson’s

Ratio

CB 2.25x3.5x24 AX 64 9.79 ( 0.08 )

CB 24x3.5x2.25 TR 64 10.70 ( 0.09 )

MB 1 x 6 x 48 AX 24 9.58 ( 0.08 ) 4.03 ( 0.13 ) 0.19

MB 48 x 6 x 1 TR 33 10.59 ( 0.09 ) 4.73 ( 0.32 ) 0.12

Type CB specimenType MB specimen

Isotropy ratio = ~1.1

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Electrical Resistivity

Specimen type

Specimen dimensions

X x Y x Z mmOrientation

No. ofTests Electric

ResistivityStandard deviation

CB 2.25x3.5x24 AX 64 11.39 ( 0.13 )

24x3.5x2.25 TR 64 10.45 ( 0.11 )

MB 1 x 6 x 48 AX 24 11.86 ( 0.04 )

48 x 6 x 1 TR 33 10.77 ( 0.05 )

Isotropy ratio = ~1.1

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Flexural Strength - Equibiaxial strength

Dim. (mm)* Orient. Valid

Tests

Normal Average (MPa)

Normal Std.Dev.

(MPa)

Weibull Scale MLE Unbiased

(MPa)

95% LB (MPa)

95% UB (MPa)

Weibull Shape MLE

Unbiased

95% LB

95% UB

6x6x0.5 Tr 30 61.49 2.44 62.52 (61.81 - 63.24) 33.3 (24.9- 44.4)

Specimen type 3SQ6

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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.

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Tensile Strength: Specimen Size Effect Validation

ID Gauge Diameter Type Orientation Quantity

Full ASTM 6.5 mm Whole piece Axial 30Full ASTM 6.5 mm Whole piece Trans 30

Intermediate 5 mm Whole piece Axial 30

Irradiation size with gauge 4 mm Whole piece Axial 30

Irradiation specimen 4 mm Epoxy glued Axial 30

Smaller than irradiation specimen 3 mm Whole piece Axial 30

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TS4 with Steel Extenders and Alignment Block Setup

Alignment block top

Steel extensor

Alignment block base

V notch Push screw

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Tensile Strength – Preliminary Results

TS6.5U Axial SpecimenX-Y Strain Gauge Reading

Poisson’s ratio: 0.13

• No significant effects of gauge diameter and epoxy-extension.

– More discussion in Katoh et al ASTM paper later this week.

Epoxy-extended Specimens

Unibody Specimens

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Data Comparison for : IGS743NHNTC vs. ORNL Pre-Irradiation Evaluation

• Reasonable agreement has been observed between data generated by NTC and ORNL

Property Unit IGS-743Catalog

IGS-743NHORNL (Tr/Ax) Remarks

Density g/cm3 1.80 1.79 CB specimen for ORNL

Flexural Strength MPa 54 - 3 point bend

Flexural Strength MPa - 61Transverse, Equibiaxial,

miniature

Tensile Strength MPa 35 35 Ø5 – 6.5 mm for ORNL

Thermal Conductivity W/m-K 128 116/126

CTE (RT-500°C) ppmK-1 4.8 4.5/5.0

Resistivity Ohm-m 12.5 10.4/11.4

Young’s Modulus GPa 10.7/9.8 Dynamic for ORNL

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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.