Two-stage modelling of hexagonal fuel assemblies vibration considering mechanical nonlinearities

The paper presents a complex modelling concept for the nuclear fuel assembly vibration caused by the coolant pressure pulsations generated by the main circulation pumps. The method is based on the two-stage modelling with the reactor's global model at the first stage and the detailed model of the particular fuel assembly at the second stage. This approach allows respecting all the relevant mechanical nonlinearities - clearances and friction in the key-groove couplings between the reactor core barrel and the pressure vessel and the internal impact or the friction interaction of the fuel assemblies. Numerical simulations allow better interpretation of monitoring data concerning the fuel burn-up