Thermohydraulics-Thermomechanics best estimate coupled approach in a rod ejection accident core calculation

Within the framework of the CEA scientific research on multiphysics and multiscale coupling in nuclear reactor modeling, our main interest lies within accidental situations that may occur in Pressurized Water Reactors (PWR). During these kinds of situations the reactor should respect three safety principles [1], i.e., control the reactivity, ensure reactor cooling and contain the radioactive material. A Rod Ejection Accident (REA) is characterized by a strong interaction between the different areas of the reactor physics (neutronics, fuel thermomechanics and thermohydraulics) and a heterogeneous deposit of Energy on the core, as well as the increase of the temperature during the transient. It might induce the failure of the fuel clad by brittle failure (Pellet Clad Mechanical Interaction) or ductile failure (ballooning of the heated clad by the fission gas). The clad is the first safety barrier that ensures the containment of the radioactive material. In this context, an accurate representation of the thermal evolution of the core is needed, through an accurate fission gas and physico-chemical modeling of the fuel pin. In this paper we focus on the exercise of an accurate thermohydraulical modeling of the core and a realistic simulation of the fuel pin behavior through an academic REA scenario.