To improve the safety and lifetime of boiling water-type nuclear fission reactors, new accident tolerant fuels are under development where a Cr-based coating is applied to the conventional Zr-alloy nuclear fuel cladding. However, an undesirable brittle intermetallic layer may form, and diffusion of elements in each metallic layer also affects the alloy properties. The stability and structural properties of the fuel coating layers were investigated under various doping conditions using first-principles calculations. This data was used to build a Cr-Zr-X thermodynamic database to be used for preliminary design of this layered nuclear fuel. The thermodynamics of the whole system was considered to predict atomic migration and intermetallic formation. Based on this data, candidate alloying elements for the Cr- or Zr-alloy are proposed that may limit intermetallic phase formation, eliminate significant volume changes that may cause microcracking, or that may improve the properties of the cladding system as a whole.