Today one of the main problems to be solved is increasing the safety of nuclear power plants (NPP). Possible shortcomings of the reactor plant (RP) can be identified by creating full-scale or large-scale prototype models for testing. There is an urgent need to create models for a more detailed study of some complex processes (flow mixing, heat and mass transfer and flow mixing under the action of dynamic forces). For example, the negative impact of these processes on the switchgear makes it difficult to ensure the natural circulation of the coolant (NCC) in all modes of operation, which could significantly increase the switchgear safety. At modern NPP this condition is not achieved either and the problem is solved by large safety factors. The purpose of this work is to evaluate the influence of external dynamic forces (EDF) on the processes of mixing of non-isothermal flows in the simulator of the core, applied to the research stand «Single-loop RP model». For the research stand we have designed a swinging platform simulating EDF. The main method for obtaining experimental data is direct layer-by-layer temperature sensing. We have also constructed a simple one-dimensional mathematical model describing these processes, based on Newton's Second Law. The adequacy of model selection has been confirmed experimentally. We have plotted graphs of temperature fronts for the experimental model and made a graphic representation of the coolant temperature field at the model entrance / exit for the dynamic mode. A mathematical equation has been obtained for describing the effect of EDF on the length of the Prandtl mixing path for the one-dimensional approximation. Based on the analysis of the results obtained, we can conclude that the external dynamic force has a negative effect on the mixing of non-isothermal flows. They change the length of the mixing path in comparison with the stationary mode by an average of 5–10 %, which, when transferred to a real NPP, can significantly affect the NCC and will need to be taken into account in the form of correction factors at the design stage.

Today, improving the safety of nuclear power plants is one of the main problems. Obviously, heat and mass transfer processes have a great influence on complex phenomena occurring in the reactor plant. Currently, special software systems are being developed that can describe these processes (Computational Fluid Dynamics (CFD)). However, they do not take into account the influence of external gravitational forces. They occur when the spatial position of an object changes. In the case of ship-based nuclear power plants, the development of technical specifications should include a mandatory requirement for trouble-free operation when affected by pitching and rolling. The paper describes the study of the effect of shipboard pitching on the mixing processes of non-isothermal flows in a small-scale model. Based on the analysis of the results obtained, it can be concluded that the external dynamic force has a negative effect on the mixing of non-isothermal flows.

Simulation of mixing flows of different temperature, density structure has important implications for the assessment of thermal reliability of reactor plants, thermo-cyclic pulsations, and safety analysis. To study the mixing model was used for the mixing, which was visualized by using imaging methods. The injection of cold water into the hot volume was examined, which simulates the flow of the coolant in the pressurized-water reactor. The obtained results have given the basis for further analysis of non-isothermal mixing flows. However, the model is still far from the real geometry of the reactor plant. The construction of a reactor reduced model with a simulation of one loop of a coolant flow with low settings has been developed for a more detailed study of the processes of non-isothermal mixing flows has planned. In the future, these data will be used in the programs of computational fluid dynamics (CFD).

The processes for mixing of non-isothermal streams essentially define the parameters of the heat-carrier on an input in a core in modes with incomplete structure of the working equipment and, as a consequence, - a heat engineering condition of a core. Besides, the task of researching the temperature pulsations accompanying practically all modes of currents for non-isothermal streams is extremely relevant, as these pulsations lead to additional thermocyclic loadings on elements of the equipment and in many cases define its resource. The paper describes the research of mixing processes for non-isothermal water coolant flows in hydraulic model of ship nuclear power plant. In several experiments, attention was paid to the mixing processes when feeding non-isothermal flows through the circulation loops located opposite of each other. To simulate the effect of external dynamic force in the form of periodic effect on the spatial orientation of the model, the ship was tested on a stand "Swinging platform". These vibrations affected the mixing processes occurring within the model. The main impact they had on the transition time, temperature gradient, vertical component of the velocity projection. In the future, these parameters will be clarified and the influence of other factors on the mixing of non-isothermal flows in the ship's nuclear power plant will be studied in more detail.