Speaker
Description
The performance of very high-temperature gas-cooled reactors (VHTRs), such as the pebble bed modular reactor (PBMR), relies on the effective retention of fission products (FPs) within the fuel. Silicon carbide (SiC), used as a primary diffusion barrier in nuclear fuel, is exposed to both FPs and helium (He) generated from alpha decay and transmutation processes. In this work, the influence of He on the migration behavior of selenium (Se) pre-implanted into SiC was investigated. Se ions were implanted into SiC at 200 keV to a fluence of 1×10¹⁶ ions/cm² at both room temperature (RT) and 500 °C. A subset of these samples was subsequently co-implanted with 17 keV He ions at a fluence of 1×10¹⁷ ions/cm² under the same temperature conditions. All samples were then annealed at 1100 °C for 5 hours under vacuum. Se implantation at RT resulted in complete amorphization of the SiC matrix, whereas implantation at 500 °C introduced damage without fully amorphizing the structure. Subsequent He implantation at RT led to the formation of He clusters (non-bubble features), associated with the aggregation of He atoms at defect sites within the damaged region, resulting in observable surface swelling. In contrast, He implantation at 500 °C promoted the formation of larger He bubbles with more swelling observed in the surface. Post-annealing at 1100 °C induced recrystallization in all samples; however, graphitization was observed in the co-implanted samples. Enhanced Se migration was detected in the co-implanted samples, indicating that He facilitates Se diffusion in SiC. Additionally, surface cavities were observed only in the co-implanted samples after annealing, likely due to surface exfoliation driven by He bubble evolution. These findings provide important insight into the role of He in modifying defect structures and enhancing fission product transport in SiC under reactor-relevant conditions
| Apply for student award at which level: | PhD |
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