Speaker
Description
The global energy crisis and the need to reduce greenhouse gas emissions have positioned nuclear power as a viable low carbon option. However, concerns remain about the release of radioactive fission products (FPs) and the long term storage of nuclear waste. In advanced reactor design like High Temperature Gas Cooled Reactor, tri structural isotropic (TRISO) fuel particles comprising a uranium dioxide kernel coated with carbon and silicon carbide (SiC) layers offer superior retention of most FPs, with SiC serving as the main diffusion barrier due to its outstanding physical and chemical properties. Nonetheless, certain FPs such as iodine,strontium, silver and cesium can escape, while selenium (Se), particularly Se-79 which is a long lived beta emitter, poses additional safety and environmental challenges due to its potential mobility at elevated temperatures.
During fission some products initially possess high energies comparable to swift heavy ions (SHIs) which may significantly affect the silicon carbide microstructure and containment of fission products. This study investigates the effects of SHIs irradiation using 710 MeV Bi ions with a maximum electronic energy loss of 33.7 keV/nm and subsequent annealing on the structural evolution and migration of Se implanted in SiC.
SiC was implanted with 200 keV Se ions at room temperature (RT) and 350 °C, followed by SHIs irradiation and sequential annealing between 1000 and 1300 °C. Microstructural changes were analyzed using Raman spectroscopy, scanning electron microscopy and transmission electron microscopy, while Rutherford backscattering spectrometry tracked selenium migration. RT implantation resulted in an amorphous layer of about 187 nm which partially recrystallized upon SHIs irradiation, while 350 °C implantation retained crystallinity with only defective layers that showed enhanced recovery after irradiation.
Annealing of RT implanted samples reduced defects and produced nanocrystalline SiC with cavities and selenium precipitates at 1200 °C. In contrast, 350 °C implantation led to nanocrystalline SiC with minor strained regions. No detectable migration of Se was observed in either the RT or 350 °C pre-implanted and irradiated samples after annealing up to 1200 °C. At 1300 °C, RT samples lost about 20% of Se, while 350 °C samples showed Se migration into bulk SiC with minimal loss.
Overall, higher implantation temperatures promoted structural recovery and stabilized dopant distribution.
