Modelling of the flow induced stiffness of a PWR fuel assembly

Nuclear industry needs tools to design reactor cores in case of earthquake. A model simulating the response of the core to a seismic excitation have been developed. Full scale tests considering one fuel assembly are performed to identify coefficients (added mass and damping) that will be used as inputs in the models. Tests showed that the axial water flow induced an added stiffness. In the paper, an expression of the fluid force responsible for the added stiffness is proposed. Numerical simulations are compared to experiments and showed good agreement.