3d simulation in the pleiades software environment for sodium fast reactor fuel pin behavior under irradiation

Overview & Synopsis

In the framework of the basic design of ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) the GERMINAL fuel performance code is developed in the PLEIADES software environment. In order to improve one dimensional modelling of GERMINAL, a 3D simulation for the SFR fuel pin behavior under irradiation has been proposed. The 3D model represents a single pellet fragment and its associated piece of cladding. The scale transfer between this single fragment model and the fuel pin scale is achieved through appropriate boundary conditions given by GERMINAL results. The 3D thermo-mechanical computation scheme is implemented in the LICOS code of the PLEIADES platform. In this approach, chemo-physical state variables are pre-computed by the GERMINAL code and are introduced in the 3D computation scheme as some input data in a two-step procedure. First studies have been achieved in order to analyse pellet-to-cladding gap closure mechanisms at the beginning of irradiation. Two mechanisms of fuel relocation have been identified through the 3D simulation. The first one is linked to the hourglass shape of the fragmented fuel pellet under thermal gradient, and the second one is induced by the mass transfer due the central-hole formation and fuel restructuration. Thanks to our 3D results, the gap closure rate given by the fuel relocation displacement model of GERMINAL can be interpreted. The next step is now to propose a full coupling formulation between fuel mass transfer model and the radial relocation displacement model.