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Multibody systems modelling and analysis are efficient tools utilizable in general tasks of nonlinear dynamics. One of the branches suitable for the application of multibody approaches is the modelling of nonlinear motion and dynamical analysis in nuclear engineering. The motion of important parts of nuclear reactors called control assemblies has to be analyzed. The purpose of these control systems is to control the power of a nuclear reactor and possibly to stop the reaction in case of an emergency state. With respect to different types of nuclear reactors, different control systems composed of various mechanical parts and transmissions can be distinguished. Generally, they can be simplified to the typical problem of a long thin rod moving through guide tubes and driven by a motor. Then the modelling approach depends on the chosen mode of operation, which can be operation (regulation) under normal conditions or a certain emergency state. The paper is focused on the control assembly of the VVER 1000 nuclear reactor. The VVER 1000 reactor is a pressurized water-cooled and water-moderated reactor consisting of a reactor pressure vessel with an interior structure and a reactor upper block with 61 control assembly drives. Under the vessel head with nozzles of the control assembly drives there is a block of protective tubes, which is above the core with 163 fuel assemblies. A moveable part of the control assembly, i.e. a rod control cluster assembly (this part is the necessary condition for stopping the nuclear reaction), is composed of a suspension bar, a spider and 18 long thin absorber rods. Two modular spatial multibody models of the LKP-M/3 control assembly of the VVER 1000 nuclear reactor were created in the alaska simulation tool and they differ in their kinematic scheme and in the number of contact positions. Both models are meant for the simulations of the control assembly moving parts drop. The first one is intended for the simulations of the rod control cluster assembly drop during the seismic event, where the total time of the drop is the significant measured and computed quantity, and the second one for investigating limit curves of deformations of fuel assembly guide tubes, at which the absorber rods still reach the lower part of the core.

APPROACHES TO THE CREATION OF MULTIBODY MODELS OF THE VVER 1000 NUCLEAR REACTOR CONTROL ASSEMBLY