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

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- dependent dimensional change of various graphite. B.T. Kelly et al, IAEA-TECDOC-1154, 2000 Dimensional change (%)

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

1.7 MV Tandetron 20A 5.1 MeV Si 2+ 10A 6.4 MeV Fe MV Singletron 10A 1.0 MeV He + DuET facility, Kyoto University DuET: Dual-beam irradiation facility for Energy science and Technology

Ion Irradiation Effects on Specimen Surface 10μm 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 Change Beam 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 SEM image Binary image “after noise reduction”

Experimental Procedure Irradiation Holder Ion Irradiation (DuET facility, Kyoto U.) Ions ： 5.1 MeVSi 2+ 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 Samples Materials 1. IG Candidate of nuclear graphite (CNG) Temperature Monitor

Comparison Unirr./Irrd. Surfaces IG ⁰C, 1.3 dpa Unirr.Irrd.Unirr.Irrd. 2μm2μm 2μm2μm 2μm2μm 2μm2μm IG ⁰C, 2.7 dpa

Unirr.Irrd. 2μm2μm 2μm2μm Unirr.Irrd. 2μm2μm 2μm2μm Candidate of nuclear grade graphite(CNG) 600⁰C, 1.3 dpa Candidate of nuclear grade graphite(CNG) 600⁰C, 2.7 dpa Comparison Unirr./Irrd. Surfaces

Number of Cracks Detected, /0.2mm 2 Size Distribution of the Surface Crack IG-110, C Unirradiated 4dpa 2.7dpa 1.3dpa Unirradiated 4dpa 2.7dpa 1.3dpa 4dpa 2.7dpa 1.3dpa IG-110, CIG-110, C Opening Area,  m 2 Unirradiated

Number of Cracks Detected, /0.2mm 2 Size Distribution of the Surface Crack CNG, C CNG, CCNG, C Opening Area,  m 2 Unirradiated 4dpa 2.7dpa 1.3dpa Unirradiated 4dpa 2.7dpa 1.3dpa Unirradiated 4dpa 2.7dpa 1.3dpa

CNG, C Unirradiated 4dpa 2.7dpa 1.3dpa Unirradiated 4dpa 2.7dpa 1.3dpa IG-110, C Number of Cracks Detected, /0.2mm 2 Opening Area,  m 2 Number of Cracks Detected, /0.2mm 2 Opening Area,  m 2 Comparison at 600 °C

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

20μm 1μm1μm 1μm1μm Microstructure of Unirradiated Surface CNGIG110

graphite Ion beam Initial stress: 14.8MPa Development on going

Unilateral support intended to release of irradiation induced residual stress in the thin irradiated region. Samples Ion 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 5 μm

Preliminary Results Compression (fixed) Straight (fixed) Straight (unfixed) 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.