Assessment of the influence of an external dynamic force on the mixing of non-isothermal flows in the reactor plant

Abstract

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.