Simulation Study On Pipe Network Characteristics Of Second Loop Main Auxiliary Steam System

Nuclear power secondary loop system,which is mainly composed of the steam system,condensate water supply system and cooling water system,is an important part of nuclear power plant.Wherein the steam system comprises the main&auxiliary steam systems and steam exhaust system.The network structure of the main&auxiliary steam systems is header pipe system,with many branches and large flow.During the design and operation process of the system,the load changes of the main and auxiliary machine and the structural changes of the pipe network may alter the flow distribution characteristics of the system.As a result,circumstances such as uneven distribution of flow,insufficient flow of some steam equipment and instable pressure of the header pipe may exist.In this paper,the main&auxiliary steam systems of the nuclear power secondary circuit system are studied.Firstly,the steady-state calculation model of the two-phase flow based on Flowmaster is used to calculate the hydrodynamic and thermodynamic characteristics of the main&auxiliary steam systems under variable working conditions.The simulation results are compared with the design values under the corresponding conditions,in order to check the rationality of the structural design of the pipe network.In view of the different steam levels of the inlet pipes of the four steam generators in the main and auxiliary steam systems,the deviation of the outlet flow rate of the four steam generators is reduced by changing the relative position of the steam inlet and the outlet of the steam pipe.Secondly,the relative location of the No.1 and No.2 steam generators is changed according to the actual situation.The asymmetric layout generated,offers the chance to study the effect of structural changes on the system parameters.Finally,the transient calculation model of the two-phase flow based on Flowmaster is used to calculate the transient hydrodynamic and thermodynamic characteristics of the main&auxiliary steam systems under variable working conditions.The aims are examining the changes in the parameters of the host entry during the switching of the working conditions;whether completing the working condition switch within the specified time;ensuring safe and stable operation of the system.The simulation results show that the outlet flow rates of four steam generators in the main&auxiliary steam systems are different.The flow distribution is adjusted by changing the position of the inlet pipe line of the steam generator in the steam header pipe.After optimizing the pipe network structure,the maximum deviation of the outlet flow value of the four steam generators is 2%.And the inlet parameters of the steam consumption equipment meet the design requirements,indicating that the optimized layout of the main&auxiliary steam systems is more reasonable.By changing the position of the No.1 and No.2 steam generator,the hydraulic loss of steam pipe network is in line with the actual requirements,but the deviation of the steam output of four steam generators is increased.During the switching of working conditions,the small-range variation of the parameters in the main&auxiliary steam systems is in line with the actual situation,which cause little impact on the equipment and guarantees stable and safe operation of the whole system.The time for steady state alteration from rated working condition to high working condition is about 18s,and the time for the opposite alteration generally completes around 40s.