Study On Influence Of Closed Loop On Performance Of Nuclear Main Pump Based On Source Term Method

As the pressure boundary of nuclear island primary circuit and the only rotating equipment,the long-term safe and stable operation of nuclear main pump plays a vital role in the nuclear island system.Nuclear main pump works in high temperature,high pressure,high speed and other bad working environment for a long time,and the internal flow is more complex.In the primary circuit of nuclear island,the nuclear main pump is connected with steam generator,reactor and pipeline,etc.,so the traditional uniform flow assumption cannot accurately simulate the fluid flow in the nuclear main pump.Therefore,it is of great significance to study the influence of the closed loop considering the input distortion on the performance of the nuclear main pump.Taking CAP1400 nuclear main pump as the research object,using the source term method respectively to 1:2.5 simplifying closed loop,1:2.5 real closed loop and 1:1 real machine for numerical calculation,obtain the nuclear main pump performance characteristics of closed loop(head,efficiency),internal flow field information(pressure field,velocity field,pressure pulsation),load information(radial force),The numerical calculation results are compared with those of the open core main pump model.The main work contents and research conclusions are as follows:(1)Using the source term method to replace the boundary conditions of the traditional open model,the numerical calculation of the 1:2.5 simplified closed loop model directly connected with the inlet and outlet sections is carried out,which proves the accuracy of the source term method in the numerical simulation calculation;At the same time,four different positions were selected in the simplified closed loop to explore the influence of source position selection on the numerical calculation results.(2)The source term method is used respectively to 1:2.5 simplified closed loop,considering the steam generator device is 1:2.5 real closed loop and 1:1 real machine to carry out the steady state calculation,get the nuclear main pump impeller in the middle section of the pressure field,velocity field,turbulent kinetic energy distribution,nuclear main pump intake flow distribution,and compared with the results open model;In the closed loop,the flow is more chaotic,and the inlet section produces the opposite vortex,so the turbulent kinetic energy increases obviously.(3)The transient calculation under 0.8Q,Q and 1.1Q conditions was carried out for the simplified closed loop and the real 1:2.5 scale loop respectively.Four monitoring points were selected at the clearance between the impeller and the guide blade and at the guide blade outlet respectively to obtain the time-domain and frequency domain information of pressure pulsation and the distribution of the radial force of the impeller,finally the results were compared with those calculated by the open model.The main frequency of pressure pulsation at the clearance between impeller and guide blade appears at the blade frequency,and the main frequency of pressure pulsation at the outlet of guide blade appears at the rotating frequency and blade frequency.The pressure pulsation in the closed circuit is higher than that in the open model,and the radial force in the closed circuit increases significantly.(4)Compared with the open structure,the closed loop can capture the flow field information closer to the actual working conditions,so as to evaluate the safety of the nuclear main pump more accurately.