Modeling And Analysis For Steam Generator Of AP1000 Feedwater Control System

In pressurized water reactor power plant,the heat exchange between reactor's primary circuit and secondary circuit is generally accomplished by Steam Generator(SG).It acts as the intersection of primary and secondary circuit.Besides transferring the heat from the reactor core carried by primary side coolant to secondary side water through U-tube,it also acts as the barrier that separates the primary and the secondary sides.The safety and reliability of nuclear power plant operation directly depends on whether the SG is working properly or not.Feedwater Control System(FWS)which is also known as SG level control System,controls the steam generator liquid level by regulating the flow rate of feedwater injecting into the SG.AS the FWS system aims to control feed water and obviously the feed water is non-linear and time-variable considering the operation environment.The dynamic characteristics of control object makes it difficult to control SG level because of the so called "false level " phenomenon.Generally,when the SG feed water flow,especially steam flow change on a wide range,there will be a "false level” phenomenon,the majority of plant emergency shutdown accidents that caused by SG are because of its own " false level” phenomenon.For foreign pressurized water reactor power plant,there is a survey indicates that more than 30% of the plant emergency shutdown accidents were due to the accidents of FWS,namely the poor control of its level.This kind of unexpected emergency shutdown accident reduces plant availability and cause huge economic losses,so the steam generator plays an important position in nuclear power plant.It seriously affects the safety and reliability of the nuclear power plant operation.Therefore,United States,which adopts the advanced passive power plant design concept,have done a lot of research by using serious of analysis software.This project mainly focus on the modeling and simulating of SG.For this report,the SG will be divide into 16 control blocks depending on its working process and medium condition.Corresponding mathematical model are to be built and will be simulated by software SIMULINK.This report gives the modeling range and further analysis of current feed water models and finally come to a conclusion.By comparing the results of simulation of SG working condition with the response curve comes from commercial software RELAP5,the mathematical model deduced by this report is proved to be accurate.The simulation result successfully reflect the varying situation of steam pressure,primary circuit outlet temperature and the level of secondary circuit,which can be treated as a guide or reference for the actual operation for SG and FWS.This simulation not only provide theoretical support but also data reference for FWS designing and improvement.