Dimensional Change of Isotropic Graphite under Heavy Ion-Irradiation

1. SEP15-18, 2013 INGSM-14 Seattle, USA Dimensional Change of Isotropic Graphite under Heavy Ion-Irradiation Sosuke Kondo Makoto Nonaka Tatsuya Hinoki Kyoto University

2. Contents • Ion-irradiation facility (DuET) at Kyoto University • Development of method for dimensional change evaluation • Results • Future work (evaluation of irradiation creep) at DuET

3. Graphite for HTGR Key Properties of Graphite Core Components Material 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 Graphite Simply, 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.

4. Objective The irradiation data should be quickly accumulated for multiple candidates to ensure stable supply of the graphite. Objective Development of the ion-irradiation method to evaluate the fluence- and temperature-dependentdimensional change of various graphite. Dimensional change (%) B.T. Kelly et al, IAEA-TECDOC-1154, 2000

5. 100 Fe-9Cr-2W V-4Cr-4Ti SiC/SiC 10 1 0.1 1500 0 500 1000 Irradiation Facilities 100dpa/day DuET Kyoto U. JOYO JNC/OARAI Graphite 20dpa/year Fluence / dpa-C 10dpa/year HFIR ORNL JMTR JAERI/OARAI 3dpa/year Temperature / ⁰C

6. DuET facility, Kyoto University • 1.7 MV Tandetron • 20A 5.1 MeV Si2+ • 10A 6.4 MeV Fe3+ DuET: Dual-beam irradiation facility for Energy science and Technology • 1.0 MV Singletron • 10A 1.0 MeV He+

7. Ion Irradiation Effects on Specimen Surface Non-Irradiated Irradiated 10μm 10μm Nuclear grade graphite, Irradiated in DuETat 400⁰C

8. Reason for Crack Size Change Beam Direction Irradiated Region Dimensional changes, both the contraction and expansion, are expressed by the change in crack size. Unirradiated Unirradiated Region Change in crack size can include the bulk information because many grains, cracks, and pores are included in the irradiated plane. In-plane shrinkage (expansion) within the irradiated region was constrained by the unirradiated region. 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. Tensile (Compression) stress was actually released by crack opening (closing).

9. Quantification of Crack Opening Area 20μm 20μm SEM image Binary image Binary image “after noise reduction”

10. Experimental Procedure Samples Materials 1. IG-110 2. Candidate of nuclear graphite (CNG) Ion Irradiation (DuET facility, Kyoto U.) Ions：5.1 MeVSi2+ Irradiation Temperatures：400, 600, 800⁰C Fluence： 1.3, 2.7, 4.0 dpa (at surface) Observation of the Irradiated Surface SEM (Carl Zeiss, ULTRA55) Evaluation of the change in crack opening area Image analysis Estimation of the dimensional change 10mm Irradiation Holder Temperature Monitor

11. Comparison Unirr./Irrd. Surfaces IG-110 600⁰C, 1.3 dpa IG-110 600⁰C, 2.7 dpa Unirr. Irrd. Unirr. Irrd. 2μm 2μm 2μm 2μm

12. Comparison Unirr./Irrd. Surfaces Candidate of nuclear grade graphite(CNG) 600⁰C, 1.3 dpa Candidate of nuclear grade graphite(CNG) 600⁰C, 2.7 dpa Unirr. Irrd. Unirr. Irrd. 2μm 2μm 2μm 2μm

13. Size Distribution of the Surface Crack IG-110, 4000C IG-110, 6000C IG-110, 8000C 4dpa 2.7dpa 2.7dpa 1.3dpa 4dpa 2.7dpa 4dpa 1.3dpa Number of Cracks Detected, /0.2mm2 1.3dpa Unirradiated Unirradiated Unirradiated Opening Area, mm2 Opening Area, mm2 Opening Area, mm2

14. Size Distribution of the Surface Crack CNG, 4000C CNG, 6000C CNG, 8000C 1.3dpa 1.3dpa 1.3dpa 2.7dpa 2.7dpa 2.7dpa Number of Cracks Detected, /0.2mm2 4dpa Unirradiated Unirradiated Unirradiated 4dpa 4dpa Opening Area, mm2 Opening Area, mm2 Opening Area, mm2

15. Comparison at 600 °C IG-110, 6000C CNG, 6000C 2.7dpa 1.3dpa 2.7dpa 4dpa Number of Cracks Detected, /0.2mm2 Number of Cracks Detected, /0.2mm2 1.3dpa Unirradiated Unirradiated 4dpa Opening Area, mm2 Opening Area, mm2

16. Dimensional Change of Ion-irradiated Regions CNG 800⁰C 800⁰C 400⁰C 600⁰C 600⁰C 400⁰C

17. Microstructure of Unirradiated Surface IG110 CNG 20μm 20μm 1μm 1μm

18. Development on going Ion beam Ion beam Initial stress: 14.8MPa graphite graphite

19. Development on going Samples Ion beam Unilateral support intended to release of irradiation induced residual stress in the thin irradiated region.

20. Measurement of the Irradiated Curvature 1 mm Laser monochrome image 3D laser scanning microscope (KEYENCE, VK-X200) 2D height profile Averaged height profile 5 μm 1 mm

21. Preliminary Results After ion-irradiation at 800°C Straight (fixed) After released from fixtures Straight (unfixed) After released from fixtures Compression (fixed) After released from fixtures

22. 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.