Design-oriented tool for Unprotected Loss Of Flow simulations in a Sodium Fast Reactor: Validation and application to stability analyses

•A fast-running tool dedicated to loss of flow transients in SFR has been developed.•It is used for safety-informed design and flow stability analyses.•Validation work on experiments and code to code verification has been carried out.•Thermal reactivity effects reduce the core melting probability from 75% to 25%.•The most influent scenario and modelling parameters have been identified.