"This project will support the ESNII (European Sustainable Nuclear Industrial Initiative) roadmap and the Strategic Research Agenda and the Deployment Strategy of SNETP (Sustainable Nuclear Energy Technology Platform) on the enhancement of Sodium-cooled Fast neutron Reactors (SFR) safety, especially towards a higher resistance to severe accidents.In the initiation phase of SFR core disruptive accidents, it is essential to investigate the impact of new core designs that may disperse core debris and minimize risks of core compaction. The available codes today have been developed in the 80’s. The objective is to develop a new European simulation code, ASTEC-Na, with improved physical models, accounting for results of recent LWR research, with modern software architecture and high flexibility to account for innovative reactor designs. It will be based on the ASTEC European code system, developed by IRSN and GRS for severe accidents in water-cooled reactors. This will allow to capitalize the state-of-the-art knowledge on SFR severe accidents.The code will evaluate the consequences of fuel pin failure conditions on materials relocation and primary system loads, and the source term produced by the migration inside the reactor of activated fission products and aerosols that may be released to the environment.The project will gather partners with strong experience on SFR safety and/or on ASTEC code. Specific SFR physical models will be developed, on the basis of outputs of the CP-ESFR FP7 project. After the elaboration of general specifications and of a validation matrix, the models will be developed, implemented into the code, validated vs. experiments (like past CABRI ones) and benchmarked with other codes. The further extension of ASTEC-Na to cover other parts of the SFR severe accidents (transition phase, fires) and to LFR will be investigated.An Education programme will include workshops as well as the secondment of young researchers in other organizations."