Owing to their superior properties, TiN and TiC have been proposed as potential fuel cladding materials for the proposed generation IV (Gen IV) nuclear energy systems. In this application they will be exposed to irradiation at elevated temperatures and should be able to retain fission products under these conditions. Xenon -135 is an unstable isotope of xenon (Xe) with a half-life of 9.2 hours and is one of the abundant fission products (FPs) of uranium in the nuclear reactor. About 5% of 135Xe is produced as FP, while 95% comes from Iodine- 135 decay. Hence its migration into fuel cladding material is vital for the success of the proposed reactors. Some investigations have been carried out on the radiation tolerance and migration behaviour of Xenon in TiN and TiC. To get more insight in the migration behaviour of Xe in TiN and TiC, the influence of irradiation needs to be understood. In this study, the effect of swift heavy ion (SHI) irradiation in the migration behaviour of Xe implanted into spark plasma sintered TiN and TiC was investigated. TiN and TiC powders were sintered by spark plasma sintering (SPS) at 1900 °C. Some of the as-sintered samples were implanted with Xe-360 keV ions to a fluence of 1.1×1016 cm-2 at room temperature (RT), and others were first irradiated with Xe-167 MeV ions to a fluence of 3.4×1014 cm-2 at RT then implanted with Xe-360 keV ions to a fluence of 1.1×1016 cm-2 also at RT. Both implanted and irradiated then implanted samples were isochronally annealed at temperatures ranging from 1100-1600 °C in steps of 100 °C for 5 hours under vacuum. Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the as-sintered samples while the implanted and the irradiated then implanted and annealed samples were additionally characterised by Rutherford backscattering spectrometry (RBS). SEM and XRD confirmed the successful sintering of the powders while RS and XPS revealed that the as-sintered TiC and TiN had vacancies (Frenkel defects) and had oxidized on the surface.
Both implantation and irradiation then implantation caused no amorphization of TiN and TiC samples. Annealing caused progressive annealing of defects in both TiN and TiC samples.
Migration of implanted Xe in TiN was governed by trapping and de-trapping of implanted Xe through defects in the implanted samples annealed at the temperatures below 1200 °C and was mainly through grain boundary diffusion towards the surface accompanied by loss at temperatures above 1200 oC. About 90% of implanted Xe was lost after annealing at 1600 °C. In the irradiated then implanted samples, the migration of Xe was mainly via fast grain boundary diffusion towards the surface accompanied by a loss at all annealing temperatures. Almost all implanted Xe was lost after annealing at 1600 °C. The diffusion of Xe in the implanted TiN samples was measured at temperatures ranging from 1100 to 1400 °C and yielded to an activation energy of Ea = (2.2 ± 0.5) × 10-19 J = 1.4 eV and pre-exponential factor of Do = (1.4 ± 0.5) × 10-16 m2/s.
The migration of implanted Xe was governed by trapping and de-trapping of implanted Xe through defects in the implanted TiC samples at annealing temperature below 1200 °C and a fast grain boundary diffusion towards the surface accompanied by loss at temperatures above 1200 °C. About 75% of implanted Xe was lost after annealing at 1600 °C. In the irradiated then implanted TiC samples, the migration of implanted Xe was due to grain boundary diffusion towards the surface accompanied by the loss throughout the annealing process. About 60% of implanted Xe was lost after annealing at 1600 °C. The diffusion of Xe in the implanted and irradiated then implanted TiC samples were determined at temperatures ranging from 1200 to 1500 oC and yielded to an activation energy of 1.4 eV and pre-exponential factor (Do) of 5.2×10-17 m2s-1 for implanted TiC and 1.6 eV and 5.2×10-16 m2s-1 irradiated then implanted TiC.
Thesis (PhD (Physics))--University of Pretoria, 2021.