Hyperbolicity and numerics in SYS-TH codes: The FONESYS point of view

The paper provides a brief overview on the state of the art of the numerical modeling in present system thermal-hydraulic codes in the framework of the Forum & Network of System Thermal-Hydraulics Codes in Nuclear Reactor Thermal-Hydraulics (FONESYS). FONESYS is a network among code developers who share the common objective to strengthen current technology and to bring technical argumentation against possible disbelief in SYS-TH codes. The aim of the FONESYS network is to highlight the capabilities and the robustness as well as the limitations of current SYS-TH codes to predict the main phenomena during transient scenarios in nuclear reactors for safety issues. This objective will be achieved primarily through the development of a strategy that aims to identify the key aspects for the improvement of SYS-TH codes and then establish a work program regarding actions to be taken to provide an answer to the needs listed in the Road Map of FONESYS network. In this regard, key topics, like the hyperbolicity, the numerical methods and some closure laws with particular reference to the modeling of some interfacial forces in the current SYS-TH codes, have been treated by the FONESYS network and are summarized in this paper.