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Helium Release in SiC Tile

Helium Release in SiC Tile. HAPL Workshop University of Rochester November 8 and 9, 2005. First Wall Armor. MeV He. vacancy. MeV He. Helium transport in CVD SiC: literature survey. Cavity Formation in CVD SiC. 1273K, 10 dpa, 600 appmHe.

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Helium Release in SiC Tile

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  1. Helium Release in SiC Tile HAPL Workshop University of Rochester November 8 and 9, 2005 First Wall Armor MeV He vacancy MeV He

  2. Helium transport in CVD SiC: literature survey

  3. Cavity Formation in CVD SiC 1273K, 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. 1673K, 10 dpa, 600 appmHe ORNL / Kyoto University

  4. 50nm 50nm Helium Transport in Irradiated CVD SiC at 1673K 60dpa 60dpa (b) (a) 1673K, 60 appmHe/dpa Irradiated surface Beam direction 50nm (c) GB 5dpa (c) SiO2 layer He distribution (a) GB (b) ORNL / Kyoto University

  5. Helium transport / retention in CVD SiC Quick 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.

  6. Weak Beam / Bright Field Image Comparison10 dpa at 1273 K, 1x10-5 dpa/s ORNL / Kyoto University • Matrix bubbles in the dual-beam irradiated sample are often clustered on <111> loops.

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