Defect-oxygen interaction in uranium mononitride surfaces: Elucidation of micro-mechanisms and prospects for multi-scale research

Uranium mononitride (UN), as the core component of uranium-based nitride modification layers, demonstrates significant potential in enhancing the corrosion resistance of nuclear materials. However, the UN layers produced in practice exhibit multiple inherent and process-induced defects, which significantly influence their initial corrosion kinetics and long-term stability in oxidising environments. The focus of this paper is the interaction between defects and oxygen behaviour in UN, with detailed analysis of defect formation mechanisms and oxidation behaviour of UN layers. The study explores the influence of defects on corrosion resistance, investigating their role as active sites or diffusion pathways. Integrating experimental and theoretical advances, the study addresses the following core issues: To begin with, extant models frequently depend on ideal surfaces and single defects, thus leaving unclear how defect synergistic effects regulate oxidation behaviour. Moreover, extant research has focused predominantly on the impact of defects on oxidation in a single direction, while the mechanism by which oxidation-induced surface reconstruction dynamically alters defect stability remains poorly understood. Lastly, a lack of multiscale predictive models exists which link atomic-scale electronic structure modifications to macroscopic oxidation kinetics. This paper posits that the integration of multiscale computational simulations, in situ characterisation, and experimental studies is imperative for the elucidation of defect-oxygen interactions. Uranium mononitride (UN), as the core component of uranium-based nitride modification layers, demonstrates significant potential in enhancing the corrosion resistance of nuclear materials. However, the UN layers produced in practice exhibit multiple inherent and process-induced defects, which significantly influence their initial corrosion kinetics and long-term stability in oxidising environments. The focus of this paper is the interaction between defects and oxygen behaviour in UN, with detailed analysis of defect formation mechanisms and oxidation behaviour of UN layers. The study explores the influence of defects on corrosion resistance, investigating their role as active sites or diffusion pathways. Integrating experimental and theoretical advances, the study addresses the following core issues: To begin with, extant models frequently depend on ideal surfaces and single defects, thus leaving unclear how defect synergistic effects regulate oxidation behaviour. Moreover, extant research has focused predominantly on the impact of defects on oxidation in a single direction, while the mechanism by which oxidation-induced surface reconstruction dynamically alters defect stability remains poorly understood. Lastly, a lack of multiscale predictive models exists which link atomic-scale electronic structure modifications to macroscopic oxidation kinetics. This paper posits that the integration of multiscale computational simulations, in situ characterisation, and experimental studies is imperative for the elucidation of defect-oxygen interactions.