Mechanical strength testing of irradiated

HTR graphite gradesM.C.R. Heijna, J.A. Vreeling

NRG, Petten

The Netherlands

INGSM-14

18 September 2013

Seattle

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Outline

• Introduction– HTR graphite– INNOGRAPH irradiation programme

• Tensile strength from diametric compression– Why?– How?

• Results– Movies!– Trends for coke, grain size, production process

• Conclusions

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HTR Graphite• Two types of (V)HTR:

• pebble bed• prismatic block

• Graphite as moderator• Structural material

Images from Wikipedia

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INNOGRAPH programme

European Commission Framework Programmes:• Retain (V)HTR knowledge• Screen properties of modern graphite grades

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INNOGRAPH programme

INNOGRAPH-1A: 750°C, 5-10 dpa

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INNOGRAPH programme

INNOGRAPH-1B: 750°C, 10-25 dpaINNOGRAPH-2A: 950°C, 4-8 dpaINNOGRAPH-2B: 950°C, 8-15 dpa

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INNOGRAPH programme

INNOGRAPH-1B: 750°C, 10-25 dpaINNOGRAPH-2A: 950°C, 4-8 dpaINNOGRAPH-2B: 950°C, 8-15 dpa

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INNOGRAPH programme

INNOGRAPH-1C: 750°C, 1-2 dpaIrradiation will be concluded this month

INNOGRAPH design• Selected irradiated samples from

“1A”and “2A” were further irradiated in “1B” and “2B”

• INNOGRAPH-1B and -2B have been assembled in the NRG hot-cells

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INNOGRAPH design• Each experiment contains 24 thermocouples and

9 dosimeter sets• Temperature controlled by gas mixture• Temperature control within ±30°C

• In the order of 180-220 samples per experiment• Sample geometry:

• 6 mm high, 8 mm diameter• Flat side with sample coding

• Samples in inert environment

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Graphite grades

Manufacturer Grade Coke Process

IG-110 petroleum iso-mouldingIG-430 pitch iso-mouldingNBG-10 pitch extrusionNBG-17 pitch vibro-mouldingNBG-18 pitch vibro-mouldingNBG-25 petroleum iso-moulding

PCEA petroleum extrusionPCIB petroleum iso-mouldingPPEA pitch extrusionLPEB Needle extrusionLPIB Needle iso-moulding

GrafTech

Toyo Tanso

SGL

Major grades for this programme

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Irradiation in HFR, Petten

• Tank-in-pool type MTR• 40 MW thermal• Operated by NRG

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Post Irradiation Examination

Data on 800 graphite samples• Dimensional change• Density• Young’s modulus• Coefficient of Thermal Expansion• Thermal conductivity• Electrical resistivity

sample recovery

measurements

data set

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Test matrix strength measurements

• Irradiation temperature 750°C

• Fine grains and coarse grains

• Pet & pitch coke• Various production

processes• Different levels of dpa’s /

volume change

• Sample selection limited by:

• Reloaded samples• Microscopy samples

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Diametric compression

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Why diametric compression?

Typical tensile test geometry INNOGRAPH geometry

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Tensile strength from diametric compression

S.P. Timoshenko, J.N. Goodier, “Theory of elasticity”, 1970H. Awaji, J. Soc. Mat. Sci. Jap. 27 (1987)C. Berre et al., unpublished

Tensile strength < Compressive strength

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Tensile strength from diametric compression

z = unique direction

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Experiment! Coarse grain graphite

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Experiment! Fine grain graphite

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Strength vs dpa; Grain size

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Strength vs dpa; Grain size

DV/V0

Scanning Electron Microscopy

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Fine grain, 0 dpaGrade C

Coarse grain, 0 dpaGrade A

Fine grain, 13.4 dpaGrade C

Coarse grain, 12.8 dpaGrade A

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Strength vs dpa; Coke

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Strength vs dpa; Process

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Conclusions

• Successful irradiation and PIE campaign concluded by demolishing samples

• Tensile strength vs. dpa trends derived from diametric compression

• At turn-around, strength doubles– Regardless of grain size, coke, production process

• Fine grained graphite stronger than coarse grained– Regardless of irradiation

• Coke and process have negligible effect on tensile strength

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Conclusions

• Successful irradiation and PIE campaign concluded by demolishing samples

• Tensile strength vs. dpa trends derived from diametric compression

• At turn-around, strength doubles– Regardless of grain size, coke, production process

• Fine grained graphite stronger than coarse grained– Regardless of irradiation

• Coke and process have negligible effect on tensile strength

Thank you for your attention!