Dimensional Change of Isotropic Graphite under Heavy Ion-Irradiation

Sosuke KondoMakoto NonakaTatsuya Hinoki

Kyoto University

SEP15-18, 2013INGSM-14Seattle, USA

Contents

• Ion-irradiation facility (DuET) at Kyoto University

• Development of method for dimensional change evaluation

• Results

• Future work (evaluation of irradiation creep) at DuET

Graphite for HTGR

Key Properties of Graphite Core ComponentsMaterial property changes which affect internal stress are

key to avoid the excessive deformation of the core components. For example, dimensional change, thermal conductivity, CTE change, modulus change, are essential for analyzing internal loads of core components.

Irradiation Performance of Nuclear Grade GraphiteSimply, the graphite formed by densely and randomly-

oriented small crystallite shows good dimensional stability. However, many candidates may have various “unirradiated”

properties, such as microstructure, graphitization degree, and pore structure, depending on the production method, such as starting material, heat treatment temperature, number of pitch infiltration.

Objective

The irradiation data should be quickly accumulated for multiple candidates to ensure stable supply of the graphite.

ObjectiveDevelopment of the ion-irradiation method to evaluate the fluence- and temperature-dependent dimensional change of various graphite.

B.T. Kelly et al, IAEA-TECDOC-1154, 2000

Dim

ensio

nal c

hang

e (%

)

Irradiation Facilities

0 500 1000 1500

Flue

nce

/ dpa

-C

0.1

1

10

100Fe-9Cr-2W V-4Cr-4Ti

SiC/SiC

Temperature / ⁰C

JOYOJNC/

OARAI

JMTRJAERI/OARAI

HFIRORNL

20dpa/year

3dpa/year

10dpa/year

DuETKyoto U.

100dpa/day

Graphite

1.7 MV Tandetron20A 5.1 MeV Si2+

10A 6.4 MeV Fe3+

1.0 MV Singletron10A 1.0 MeV He+

DuET facility, Kyoto University

DuET: Dual-beam irradiation facility for Energy science and Technology

Ion Irradiation Effects on Specimen Surface

10μm10μm

Non-Irradiated Irradiated

Nuclear grade graphite, Irradiated in DuET at 400⁰C

Unirradiated

1. In-plane shrinkage (expansion) within the irradiated region was constrained by the unirradiated region.

2. If the change in crack size was absent, the in-plane tensile (compression) stress might be accumulated in the irradiated region with increasing in DPA.

3. Tensile (Compression) stress was actually released by crack opening (closing).

Reason for Crack Size ChangeBeam Direction

Irradiated Region

Unirradiated Region

Dimensional changes, both the contraction and expansion, are expressed by the change in crack size.

Change in crack size can include the bulk information because many grains, cracks, and pores are included in the irradiated plane.

Quantification of Crack Opening Area

20μm

20μmSEM image

Binary image

𝐷𝑖𝑚𝑒𝑛𝑠𝑖𝑜𝑛𝑎𝑙 h𝑐 𝑎𝑛𝑔𝑒 , Δ 𝐿/𝐿（%）≈Δ 𝐴𝑤

❑

𝐴𝑤𝑢𝑛𝑖𝑟𝑟 ×100×

12

Binary image“after noise reduction”

Experimental Procedure

Irradiation Holder

Ion Irradiation (DuET facility, Kyoto U.)Ions ： 5.1 MeVSi2+

Irradiation Temperatures ： 400, 600, 800⁰CFluence ： 1.3, 2.7, 4.0 dpa (at surface)

Observation of the Irradiated SurfaceSEM (Carl Zeiss, ULTRA55)

Evaluation of the change in crack opening areaImage analysis

Estimation of the dimensional change

10mm

SamplesMaterials1. IG-1102. Candidate of nuclear graphite (CNG)

Temperature Monitor

Comparison Unirr./Irrd. Surfaces

IG-110600⁰C, 1.3 dpa

Unirr. Irrd. Unirr. Irrd.

2μm 2μm 2μm 2μm

IG-110600⁰C, 2.7 dpa

Unirr. Irrd.

2μm 2μm

Unirr. Irrd.

2μm 2μm

Candidate of nuclear grade graphite(CNG)600⁰C, 1.3 dpa

Candidate of nuclear grade graphite(CNG)600⁰C, 2.7 dpa

Comparison Unirr./Irrd. Surfaces

Num

ber o

f Cra

cks D

etec

ted,

/0.

2mm

2

Size Distribution of the Surface Crack

IG-110, 4000C

Unirradiated

4dpa

2.7dpa

1.3dpa

Unirradiated

4dpa

2.7dpa

1.3dpa

4dpa

2.7dpa

1.3dpa

IG-110, 6000C IG-110, 8000C

Opening Area, mm2 Opening Area, mm2 Opening Area, mm2

Unirradiated

Num

ber o

f Cra

cks D

etec

ted,

/0.

2mm

2

Size Distribution of the Surface Crack

CNG, 4000C

CNG, 6000C CNG, 8000C

Opening Area, mm2 Opening Area, mm2 Opening Area, mm2

Unirradiated

4dpa2.7dpa

1.3dpa

Unirradiated

4dpa

2.7dpa

1.3dpa

Unirradiated

4dpa

2.7dpa1.3dpa

CNG, 6000C

Unirradiated

4dpa

2.7dpa

1.3dpa

Unirradiated

4dpa

2.7dpa

1.3dpa

IG-110, 6000C

Num

ber o

f Cra

cks D

etec

ted,

/0.

2mm

2

Opening Area, mm2

Num

ber o

f Cra

cks D

etec

ted,

/0.

2mm

2

Opening Area, mm2

Comparison at 600 °C

0 1 2 3 4 5 6-1

-0.8

-0.6

-0.4

-0.2

0400°C600°C800°C

DPA

Dim

ensi

onal

Cha

nge,

%

0 1 2 3 4 5 6-1

-0.8

-0.6

-0.4

-0.2

0400°C600°C800°C

DPA

Dim

ensi

onal

Cha

nge,

%

IG-110

800⁰C

600⁰C

400⁰C

800⁰C

600⁰C

400⁰C

CNG

Dimensional Change of Ion-irradiated Regions

20μm20μm

1μm1μm

Microstructure of Unirradiated Surface

CNGIG110

graphite

Ion beam Ion beamInitial stress: 14.8MPa

Development on going

Unilateral support intended to release of irradiation induced residual stress in the thin irradiated region.

SamplesIon beam

Development on going

3D laser scanning microscope(KEYENCE, VK-X200)

Measurement of the Irradiated Curvature

Laser monochrome image

2D height profile

Averaged height profile

1 mm

1 mm

5 μm

Preliminary Results

Compression (fixed)

Straight (fixed)

Straight (unfixed)

After released from fixtures

After released from fixtures

After released from fixtures

After ion-irradiation at 800°C

Summary & Conclusions

We tried to evaluate the dimensional stability of graphite using ion-irradiation.

Results- Ion irradiation modified the surface-crack size due to the constraint by the

unirradiated region.- The T and DPA dependence of the dimensional change estimated appear

to be reliable considering the neutron irradiation data.Conclusions- Ion-irradiation method can be a quick tool for evaluating the dimensional

stability of the nuclear grade graphite.- Further tests for various graphite are essential because all the nuclear

graphite may not show the same dimensional stability.Future work- Modify the method (if necessary,) and extend data beyond TA.- Develop the ion-irradiation-creep testing method.