Nitride coatings on nuclear fuel rods offer improved water corrosion and debris fretting resistance in Boiling Water Reactor (BWR) oxidizing environments. Finding an adequate coating is particularly difficult due to the water chemistry, ruling out the solution adopted by the Pressurized Water Reactor (PWR) community, i.e. metallic chromium. In addition, if oxidation resistance is required, the main drive for BWRs is debris and grid- to-rod fretting resistance, as they cause most of the unplanned outages. Industry has started a large global effort to identify the most promising candidates and managed to down select a few candidates, based on separate effect testing only. However, the physical mechanisms at play are not well understood, and this is needed to predict long-term performances as well as to optimize further the coating composition and microstructure. This PhD project aims to model the hypotheses explaining the improved performances using first-principles modelling. It takes advantage of the ongoing projects with Linköping University (FUNMAT-II, deposition) and Chalmers Technical University (CTU)(characterization), as well as an international irradiation campaign and autoclaves to understand the corrosion reaction and suggest optimized coatings to be tried out. A successful outcome of the project consists of a mechanistic model of oxidation based on composition, used to suggest improvements to the coating composition and deposition methods, supporting new BWR build in Sweden. This project is supervised by professor Pär Olsson, KTH SCI, Division of Nuclear Science and Engineering