This document is conceived as an overview of my research work on defects stability and kinetics in two materials of interest in nuclear science and for many other application domains : silicon dioxide and silicon carbide. The preliminary chapter (page ix) is an extended summary in french of chapters 1,2,3,4, followed by a four years project playing the role of a conclusion. Chapter 1 describes the context, introduces the approach and explains the choice of silicon dioxide and silicon carbide. Chapter 2 discusses several approximations and specific issues of the application of Density Functional Theory to point defects in non-metallic materials for the study of defects energetics and diffusion. Chapter 3 is devoted to native defects in silicon dioxide and the understanding of self-diffusion in crystalline and amorphous SiO2. It discusses achievements and failures of DFT in semilocal approximations in connection with the interpretation of some notable experimental results. Chapter 4 summarises the work that I have done on native defects and palladium impurities in silicon carbide, with a focus on kinetic properties controlling the annealing of stoichiometric defects, Frenkel pairs, and silicon vacancies, as well as the diffusion of Pd impurities. A conclusion 5 closes the main part of the document, written in english. Appendixes include a compilation of defect data for silicon carbide (A.1), a Curriculum Vitæ (B, in french) and a selection of articles (C).