抄録
Control assemblies used in nuclear reactors are commonly based on a certain motor driving a control rod composed of absorber (and fuel) part(s). They allow to control a chain nuclear reaction in a reactor core. The multibody model of the LKP-M/3 control assembly of the VVER 1000 nuclear reactor is presented and some problems in the stage of its parameters tuning are emphasized (the scheme of the VVER 1000 plant layout is given in Fig. 1). The model is suitable for the investigation of the control assembly dynamic response in the course of the drop of "falling" structural parts (called rod control cluster assembly). The breakdown state occurs e.g. during an earthquake. The multibody model includes the influences of the pressurized fluid and the contacts and the impacts of the rod control cluster assembly with the adjacent structural parts inside the reactor. The multibody model including all special features was created in the alaska simulation tool. The presence of the flowing medium has the essential influence on the vertical motion of "falling" structural parts. The way of the vertical hydraulic resistance coefficient C_V determination is the main topic of the paper. This coefficient influences the resistance force acting against the vertical motion of the rod control cluster assembly and represents the influence of the shape of the body moving in fluid, the influence of fluid viscosity, which can be relatively significant especially in case of the rod control cluster assembly motion, and also the influence of the higher resistance force due to the limited space for the fluid movement. In this specific case the vertical hydraulic resistance coefficient C_V must be determined on the basis of comparing the experimentally assessed and the calculated times of the rod control cluster assembly dropping down.
