Helium Release in SiC Tile

First Wall Armor

vacancy

HAPL WorkshopUniversity of RochesterNovember 8 and 9, 2005

MeV He

MeV He

Ref Material He conc. Exp.Type T-irr.(C) T-imp.(C) T-ann.(C) t-ann.(hr)

1 CVI SiC matrix 1000 appm imp. RT, 1000 1050 1 Large bubbles on GBs, small bubbles clustered

2 4H-SiC 15 at% imp. 227, 600 900 High density bubbles on GBs and in matrix

3 4H-SiC 1.6 at% imp. RT 1500 Huge matrix cavities

4 CVI SiC matrix 2500 appm imp. 900 Bubbles on matrix/IP boundaries, no matrix bubbles

5 Sintered alpha 1700 appm neutron 300 isochronal 1 TDS peaks at 1000, 1300 & 1800C

6 CVI SiC matrix 1300 appm dual-ion 800 Matrix and GB bubbles

6 CVI SiC matrix 1300 appm dual-ion 1000 GB bubbles

6 CVI SiC matrix 1300 appm dual-ion 1300 Large GB bubbles

7 CVI SiC matrix 10000appm imp. 100 1400 1 Large GB bubbles

8 CVD SiC 6000 appm dual-ion 1400 Matrix and GB bubbles, large bubbles on surface below silica layer

9 CVD SiC 600 appm dual-ion 1000 High density matrix bubbles and some GB bubbles

9 CVD SiC 600 appm dual-ion 1400 Matrix and GB bubbles

Helium transport in CVD SiC: literature survey

1 J. Chen, et al Ceram.Int. 26 (2000) 513-5162 C.H. Zhang, et al J.Appl.Phys., submitted (2003)3 M.F. Beaufort, et al NIM-B186 (2002) 218-4 H.W. Scholz, et al JNM 258-263 (1998) 1572-5 Y. Pramono et al J.Nucl.Sci.Tech. 40 (2003) 531-6 S. Miwa, et al ?, submitted (2005)7 A. Hasegawa, et al JNM 264 (1999) 355-8 S. Kondo, et al Fusion Sci. Tech. 44 (2003) 181-9 S. Kondo, et al Mater.Trans, submitted?

1273K, 10 dpa, 600 appmHe

1673K, 10 dpa, 600 appmHe

•At 1273K, helium mostly stays within the matrix in nano-sized bubbles on stacking faults and other types of defects.

•At 1673K, helium forms larger bubbles on grain boundaries. Smaller bubbles are also present.

ORNL / Kyoto University

Cavity Formation in CVD SiC

50nm

SiO2 layer

(b)

50nm

(c)

GB

Irradiated surface

Bea

mdi

rect

ion

He distribution

(b)

(c)

GB

50nm

(a)

(a)60dpa 60dpa

5dpa

1673K, 60 appmHe/dpa

Helium Transport in Irradiated CVD SiC at 1673K

ORNL / Kyoto University

Helium transport / retention in CVD SiCQuick summary:•At < ~800C, helium mostly stays within matrix.•At 1000 - 1300C, majority of helium goes to grain boundaries.•At 1400C, substantial pipe-diffusion and GB diffusion of helium

to free surface occur.•Without sufficient atomic displacement, blisters develop and

lead to exfoliation. The situation for SiC is very similar to where we were with tungsten a few years ago….

Vacancy - helium interactions:•Helium-vacancy complexes easily form, similar to metals. •TDS measurement indicates He release at temperatures

consistent with vacancy diffusion

Dislocation - helium interactions: •Likely key mechanism of long-range helium transport. •Understanding is currently poor.

Weak Beam / Bright Field Image Comparison

10 dpa at 1273 K, 1x10-5 dpa/s

•Matrix bubbles in the dual-beam irradiated sample are often clustered on <111> loops.

ORNL / Kyoto University