Controlling the migration of implanted cesium in silicon carbide using zirconium nanolayer

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 cm⁻². 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.