HEMERA: a 3D computational chain for PWR safety analysis

In the framework of their collaboration to develop a system to study reactor transients in 'safety-representative conditions', IRSN and CEA have launched the development of a fully coupled 3D computational chain, called HEMERA (Highly Evolutionary Methods for Extensive Reactor Analyses), based on the French SAPHYR code system, composed by APOLLO2, CRONOS2 and FLICA4 codes, and the system code CATHARE. It includes cross sections generation, steady-state, depletion and transient computation capabilities in a consistent approach. Multi-level and multi-dimensional models are developed to account for neutronics, core thermal-hydraulics, fuel thermal analysis and system thermal-hydraulics, dedicated to best-estimate simulations and sensitivity analysis. Currently Control Rod Ejection (REA) and Main Steam Line Break (MSLB) accidents are investigated. The HEMERA system is presently applied to French PWR. The present paper outlines the main physical phenomena to be accounted for in such a coupled computational chain with significant time and space effects. A selection of results is presented along with a comparison of the available levels of simulation 3D, ranging from assembly-wise to pin-wise in the core. (authors)