Correlation Research Between Internal Flow And Weak Cavitation Characteristics Of Canned Nuclear Reactor Coolant Pump

At present,China's demand for energy is increasing,and it is imperative to develop and utilize nuclear energy in industrial production.Meanwhile,nuclear power has a obvious advantage over other energy sources.In a complete nuclear power plant system,the nuclear reactor coolant pump is a high-speed rotating power equipment,and its stability and operational reliability are of great significance to prevent nuclear leakage accidents.However,when the failure of the second and third circuits in the system causes the coolant temperature to be high for a long time and the core cooling effect is insufficient,the nuclear main pump could easily occur cavitation,which leads to a decrease in its external characteristics and seriously affects its safe operation.In this research,a model pump with a contracted ratio of 0.4 is taken as the research object.The internal flow characteristics of the nuclear main pump are discussed and studied in depth by the combination of numerical calculation and experiment.At the same time,the internal cavitation flow characteristics and the change of external characteristics of the nuclear reactor coolant pump under weak cavitation state are analyzed.On the basis of the above analysis,the cavitation cognition method and the influencing factors of cavitation are summarized.The main research contents and analysis are as follows:1.Analyzing the internal flowing characteristics of shielded nuclear reactor coolant pump under multiple operating conditions.The three-dimensional incompressible turbulent flow field of model pump under different flow conditions is simulated by constant value.The results show that with the impeller inlet to the outlet intermediate flow line position change,the static pressure value at the inlet of the impeller is the smallest.The static pressure value of the annular casing outdoor wall is the largest.The reason is that the continuous expansion of the flowing passage leads to the continuous increase of the static pressure value.After the relative position of the blade streamline is 0.8,the pressure of the fluid shows an obvious fluctuation.The main reason is that there is interference at the interface between the impeller blade and the vane blade and there is a pressure difference between the impeller blades.At the same time,as the flow rate increases,the velocity gradient in the vane reduces primarily and then increases.In the non-design condition,the velocity gradient in the vane is larger,and the velocity gradient is the smallest in the design condition.It shows that the hydraulic model is stable and uniform under rated flow conditions.In addition,the distribution of turbulent energy is the most reasonable under the design conditions.The energy loss is also the smallest,which indicates that the hydraulic performance is optimal under the design conditions.2.Study on the law of variation of external characteristics and internal flow characteristics during the cavitation evolution of the shielded nuclear reactor coolant pump.By analyzing the four weak cavitating conditions of the nuclear reactor coolant pump,theinternal cavitation flow characteristics are analyzed and the causes are analyzed.The results show that due to the large peripheral speed at the rim of the impeller inlet,the low pressure zone is first generated at this point,and then expands along the rim of the blade to the middle of the blade along the direction of the main flow of the blade until it occupies the entire suction surface of the blade while the middle flow line of the blade The upper load distribution shows a trend from increasing to decreasing.With the continuous evolution of cavitation,the blade load force and head are gradually reduced.In the case of weak cavitation,the flow of the air bubbles has a hindrance effect on the flow of the fluid,which affects the smoothness of the flowing;at the same time,the viscous viscosity tends to increase first and then decrease before the critical cavitation state.The bubble volume fraction distribution of the impeller suction surface is consistent with the distribution of the low pressure region.After the cavitation occurs,the pressure on the suction side of the blade is significantly reduced.The functional force of the blade on the fluid is greatly weakened,and finally the external characteristic of the model pump is degraded.In addition,it was found during the research that when the nuclear reactor coolant pump was in the stage of weak cavitation,although the nuclear reactor coolant pump was able to operate normally and the head and efficiency did not change significantly.Its internal cavitation had already occurred,so the other scholars should be carried out for the cavitation inception of nuclear reactor coolant pump.The concept of cavitation and the expression of cavitation number and the judgment method of cavitation and its influencing factors are induced.The main conclusions are as follows:(1)The judging methods of cavitation are mainly nine methods: cavitation number method,system minimum pressure method,bubble dynamics method,autocorrelation-wavelet analysis method and maximum stress criterion method,etc.;(2)The main factors affecting cavitation are gas core content and its distribution,fluid viscosity,pressure and pressure gradient,and so forth.This section expects that practitioners of fluid machinery and scholars interested in cavitation problems will clear their minds on this issue and hope to recognize and understand the cavitation mechanism of fluid machinery in the near future.