Optimum Design Of AP1000 Nuclear Reactor Coolant Pump Coast-down Model In Accident

In this paper,the coast-down characteristics of nuclear reactor coolant pump are studied by means of theoretical analysis,numerical simulation and experimental method.The coast-down process is optimized from the aspects of hydraulic performance and torque performance.The effects of moment inertia and pipe resistance on the coast-down transition process are analyzed.And the effects of different moment inertia moments on the internal flow and dynamic characteristics in impeller during coast-down transitional process are explored,the mathematical model of coast-down process is established according to the geometric parameters of impeller based on this.The main research contents and achievements are as follows:1.According to the distribution of energy stored in rotating inertia of coast-down transitional process in the unit,the optimized hydraulic performance of the nuclear reactor coolant pump is proposed to reduce the energy loss in the impeller during coast-down process and to extend the coast-down time.After referring a large number of documents,the diameter of the impeller inlet and outlet,the impeller exit angle,the impeller blade number,the blade wrap angle,the blade outlet width,the blade outlet angle,and the area ratio are selected as the optimization parameters to do orthogonal test.2.Pro/E software and CFD software are used to complete the three-dimensional modeling and external characteristic calculation of different impeller geometric parameters.Through correlation analysis,partial correlation analysis and path analysis of the numerical simulation results,the main geometrical parameters affecting the hydraulic performance and the direct and indirect effects of the geometric parameters of the impeller on the hydraulic performance in the nuclear reactor coolant pump are obtained.Combining the results of the partial correlation analysis and the path analysis,the combination of optimal impeller geometric parameters are ? = 23,?₂ = 30,? = 115,Z = 5,b₂ = 200,D₂ = 770,D0 = 555,Y = 1.002.The combination impeller of the optimal structure parameters is verified by the experiment,the results showed that the coast-down time is longer than that of the original impeller.3.The effects of different inertia and different pipe resistance on the coast-down transition process are analyzed by the construction of hydraulic prototype coast-down test bench.Through the analysis of the test results,we can see that in the process ofcoast-down,the gradient of the head is the fastest,the flow rate is the slowest,while the rotating speed is in the middle of them.The pipe resistance and the moment inertia have different effects on the coast-down transition process: the pipe resistance has little effect on the rotational speed during the coast-down transition,while it affects the flow and the head much.The moment inertia has a greater impact on rotating speed,flow rate and head.4.In order to study the influence of different moment inertia on the hydraulic characteristics and dynamic characteristics of the impeller on coast-down process,MATLAB software is used to fit different corresponding formula about rotating speed and time,flow rate and time corresponding with moment inertia.The fitting formula is used as boundary condition in CFX to do the unsteady calculation.The results show that the moment inertia has great influences on hydraulic characteristics and dynamic characteristics of the impeller,the larger the moment inertia is,the smaller the descending gradient of corresponding hydraulic characteristics and the dynamic characteristics of the impeller are.The smaller the moment inertia,the greater the descending gradient of the hydraulic characteristics and dynamic characteristics of the impeller.5.Through the orthogonal test and CFX numerical simulation,the results of the torque coefficient of six coast-down conditions corresponding to the combination of 18 sets of impeller geometric parameters are obtained.The relationship between the combination of the geometric parameters and the torque coefficients of the impeller is calculated by using multidimensional analysis,and also the regression equation between the torque coefficient and the geometrical parameters of the impeller and the combination of the optimal impeller geometric parameters are obtained.The mathematical model in coast-down process of impeller geometric parameters,moment inertia,rotation speed and time are established by principal component analysis.The correctness of the mathematical model is verified by nuclear reactor coolant pump cut-off simulation test stand in Flowmaster.The results show that: the difference between the speed variation curve in the coast-down process and the curve of the Flowmaster reactor coolant pump cut-off test stand is very small,which shows that the mathematical model has good prediction on reactor coolant pump of different impeller geometric parameters.6.The results show that the hydraulic optimization model can reduce the energyloss in coast-down process by improving hydraulic characteristics at the designed point and improve the torque performance by calculating the hydraulic characteristics and the inertia characteristics of the model.The optimization model is used to improve the coast-down characteristics of the high efficiency region of the reactor coolant pump to the small flow region.The comparison in the two models shows that the torque performance optimization model is better than that of the hydraulic optimization model in the aspect of improving coast-down performance.