Research On Distortion Inflow Model Of Reactor Coolant Pump And Its Performance Influencing Mechanism

China has independently developed the third-generation nuclear power technology HPR1000,compared with the traditional second-generation nuclear power technology,this new technology has adopted effective passive safety measures based on active safety,which is currently one of the most popular third-generation of nuclear motors in the nuclear power market.In HPR1000,the reactor coolant medium passes through the Steam Generator?SG?and a long pipe with two elbows then enters the reactor coolant pump?RCP?,which generates a distorted inflow at the pump inlet and eventually adversely affects the RCP performance and system stability.However,in the previous studies of RCP at home and abroad,few of them have considered the influence of the SG channel head and the outlet elbow on its performance,and the quantitative statistics on the development of inflow distortion in the elbow is not available.Therefore,in this dissertation,a combination of experimental research and numerical simulation is used and the coupling effect between the RCP,the SG channel head and the pipe elbows is considered to comprehensively studied the influences of distorted inflow on the RCP.Firstly,three calculated models are selected according to the different inflow conditions,and these models are numerically simulated using the CFD method then the steady calculation results and the transient flow field are obtained.The ZH-65 SG and the RCP are scaled-down in reasonable scale factor,modeling and meshing of the whole fluid domain geometry,and determining the appropriate number of meshes through mesh independence verification.Under uniform inflow condition,the steady calculation results of the scaled-down model pump are compared with the experimental results and the numerical calculation results are in good agreement with the experimental results,indicating the high accuracy of the selected calculation model and numerical parameter settings.Secondly,the steady flow field in front of the pump inlet is analyzed.Different sections of the inlet pipe were used to investigate the flow development in the pipeline,and the curve of the inflow distortion pipeline was obtained.The results show that the flow at the outlet of the lower head of the steam generator has been disturbed,producing obvious Dean Vortices in the two elbows.A large pressure gradient is generated nominal flow in the pump inlet and obvious flow separation phenomenon is observed,and the circumferential symmetry of the inlet flow field is destroyed.Large-scale inflow distortion is mainly caused by the inlet bend,which is more susceptible to structural changes,and the distortion rule is more obvious.It shows more pronounced disorder trend along the flow direction.It has weak local fluctuations,but the overall presentation Stable trend.The lower head makes the inlet flow of the elbow subject to small and medium scale disturbances.In addition,the inflow distortion causes a non-uniform mass flow rate distribution in the impeller flow channels,resulting in a non-uniform pressure distribution at the blade inlet along the Circumference.The performance of the nuclear main pump is greatly affected by inflow distortion.Under the design conditions,the head is reduced by 4%and the efficiency is reduced by 4.2%.At 1.3Q_opt,the head and efficiency are reduced by 15%,and the decline rate has a positive correlation with the mass flow rate.Finally,the transient characteristics of the pump under nominal flow condition are analyzed based on steady calculations.In the case of distorted inflow conditions,the peak value of 1-time blade frequency pulsation at the blade inlet is much larger than that of uniform inflow conditions and the same difference also appears in the range of higher than 5 times the blade frequency indicating the flow gets more unstable.Due to the asymmetric pressure distribution,the amplitudes of the radial force and the axial force on the impeller are increased,and the fluctuation is more severe.Under the condition of distorted inflow,vortices with a large distribution range and size appear in the impeller,blocking the flow channel and reducing the working force of the blade,meanwhile the development of the vortex group is self-similar.