Browsing by Author "Abdalla, Z.A.Y."
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- Encapsulating nuclear fuel kernels (i.e., uranium) in thin films, such as silicon carbide (SiC) and carbon allotropes, prevents the release of most radioactive fission products. Since SiC fails to retain cesium (Cs) within the fuel structure, the present study investigates the benefits of combining chemically stable SiC and zirconium (Zr) layers to prevent the escape of Cs from nuclear fuels. Polycrystalline SiC samples were implanted with 300 keV Cs ions at room temperature (RT) to a fluence of 1 ×1016 cm2. Selected as-implanted SiC samples were then coated with a 150 nm thick Zr layer. The annealing of the as implanted and coated samples was performed in vacuum at temperatures from 900 to 1000 ◦C, which is similar to the normal reactor operation temperatures. Our investigations show that the annealing of the as-implanted, uncoated SiC samples, at 900 and 1000 ◦C indeed leads to the diffusion of Cs atoms through the SiC surface with retentions of 47 ±5 % and 26 ±5 %, respectively. On the other hand, annealing of the coated samples at 900 ◦C resulted in the migration of Zr atoms toward the SiC layer and formation of cesium zirconate (Cs2ZrO3). However, annealing at a higher temperature (i.e., 1000 ◦C) resulted in the sublimation of Cs2ZrO3 and the formation of zirconium carbide (ZrC) in Zr-SiC samples, resulting in different Cs loss mechanisms than in SiC samples. Therefore, a Zr-SiC double layer may not be beneficial for maintaining Cs within the fuel structure when reactor operation temperatures approach the melting point of Cs2ZrO3, which is 1010 ◦C.
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- In this work the effect of swift heavy ions (SHIs) (710 MeV Bi51+) irradiation and annealing on selenium (Se) pre- implanted silicon carbide (SiC) was investigated. SiC samples were implanted individually with 200 keV Se ions to a fluence of 1 ×1016 cm2 at both room temperature (RT) and 350 ◦C. Following this, some pre-implanted samples were irradiated at RT with 710 MeV Bi51+ions to a fluence of 1 ×1013 cm2. These irradiated samples then underwent sequential annealing at temperatures ranging from 1000 to 1200 ◦C, in 100 ◦C increments, for 10 h. The samples were characterized using Raman, SEM, TEM, and RBS. Sequential annealing of the RT pre- implanted and then irradiated sample up to 1200 ◦C led to recrystallization of the highly defective SiC layer into strained nano-crystalline SiC with cavities, accompanied by the formation of Se precipitates. In contrast, sequential annealing of the 350 ◦C pre-implanted and then irradiated sample up to 1200 ◦C also caused recrystallization of the defective SiC layer into nano-crystalline SiC, but with minor strained regions. No loss or migration of Se was detected in either the RT or 350 ◦C pre-implanted samples following SHIs irradiation and annealing up to 1200 ◦C.
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- The effect of helium (He), silver (Ag) and strontium (Sr) ions implantation and annealing on the surface and structural properties of SiC as well as the migration of Ag and Sr was investigated in this study. Ag and Sr were sequentially implanted at 360 keV and 280 keV, respectively, each to a fluence of 2 × 1016 cm−2 at 600 °C. Some dual implanted (Ag + Sr-SiC) samples were additionally implanted with He of 17 keV to a 1 × 1017 cm−2 at 350 °C, forming triple-implanted samples (Ag + Sr + He-SiC). Both dual and triple implanted samples underwent isochronal annealing at 1100, 1200, and 1300 °C for 5 h. Ag, Sr and He implantation introduced defects in both dual and triple implanted samples. However, triple-implanted samples developed surface blisters and holes due to the migration of He bubbles. At 1100 °C, partial recovery of structural damage was observed in both dual- and triple-implanted samples, but graphite formed in the latter, and holes persisted. At higher temperatures (i.e., 1200 and 1300 °C), dual-implanted samples showed significant structural recovery, whereas the graphite in triple-implanted samples impeded the healing of defects. Depth profiling revealed minimal changes in Ag and Sr distributions and concentrations in dual-implanted samples post-annealing up to 1300 °C. However, triple-implanted samples lost ∼20 % of Ag and Sr at 1100 °C due to sublimation via holes. At 1200 and 1300 °C, no further losses occurred, but Ag and Sr migrated toward the surface. These findings suggest that He implantation promotes the formation of holes in SiC, facilitating the loss of Ag and Sr at 1100 °C. Additionally, He-induced defects enhance the migration of Ag and Sr toward the surface during annealing at 1200 and 1300 °C.
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