Sodium-cooled fast reactors (SFRs) remain the favorite candidate in France for a Generation IV (Gen IV) reactor fleet to be deployed within this century. Compared with earlier generations (Phénix, Superphénix, and European fast reactor), Gen IV SFRs require attractive economics together with enhanced safety and nonproliferation criteria. An innovative approach named Mathematical Estimation of Transients for Reactor design Orientation (METRO) has been developed with the objective of taking into account both SFR core economic performance and SFR transient incident behavior at an early stage of the core design process. Loss-of-flow, loss-of-heat-sink, and overpower transients are evaluated. Simplified modeling of transients has been developed and benchmarked against reference calculations with satisfactory results. The METRO approach to assessing the efficiency of design orientations is described in the following and applied to a carbide-fueled reactor core.