Thermal-Hydraulic Characteristics Simulation Study On Steam-Water Pipeline Of Second Loop System

The main auxiliary steam system and the coagulation water supply system are two important subsystems for the normal operation of the nuclear power second-loop system.The main and auxiliary steam systems have complex piping layouts.Properly reducing the diameter of the main steam main pipe can reduce the cost and save space.In the coagulation and water supply system,when the system runs in a variable condition and suddenly closes the valve and stops the pump,it will cause changes in the flow and pressure in the system.When the change is too strong,the equipment in the system will be damaged.Therefore,it is of great significance to study the thermal hydraulic characteristics of the steam pipe network and the pressure fluctuations of the water hammer in the condensate feed water system.In this paper,the main and auxiliary steam systems and the coagulation and water supply systems in the nuclear power second-loop system are taken as the research object,and the steady-state calculation model of the flow calculation software,Flowmaster,is used to perform the thermal-hydraulic calculation of the main and auxiliary steam systems and the coagulation and water supply systems.Establish the rationality of the calculation model.In the main and auxiliary steam systems,in the steady state operation of each working condition,the diameter of the main tube is reduced to a value slightly larger than the diameter of the largest branch tube.At this time,the changes in the flow rate in the mother tube and the inlet pressure of the equipment after the parent tube are studied.Utilize the transient calculation model of Flowmaster software to dynamically simulate the variable conditions of the condensate system and add PID control elements to the system to control the water level and valve opening in the auxiliary condenser,main condenser and deaerator to ensure the system The equipment operates safely.The water hammer phenomenon of the feedwater control valve in the water supply system was quickly shut down and stopped.The pressure fluctuation amplitude and duration were observed.The measures to reduce the pressure fluctuation were analyzed and proposed to reduce the water hammer phenomenon.Conclusion: When reducing the diameter of the main pipe in the main and auxiliary steam systems,the value of the resistance loss is very small due to the large outlet pressure value of the steam generator in the system and the relatively short length of the pipe connecting the main pipe and the subsequent equipment.Therefore,under the steady-state operating conditions,the diameter of the parent tube is changed and the pressure at the inlet of each device is not changed significantly.The diameter of the parent tube can be reduced.When the condensate water system operates under variable operating conditions,the control element regulates the regulating valve so that the deviation of the water level in the auxiliary condenser,the main condenser and the deaerator is within 1%,and the equipment operates safely.In the water supply system,the pipeline will produce significant pressure fluctuations when the feedwater control valve and the feedwater pump are quickly shut off.When closed within 1s,the pressure fluctuation value at the front of the valve is as high as 4.88 MPa.The pressure fluctuation value at the front of the pump is about 1.44 MPa.With the prolongation of the closing time of the valve or the water pump,the peak value of the water hammer pressure gradually decreases,indicating that the time for stopping the pump of the valve or the water pump as much as possible can effectively reduce the water hammer pressure.At the same time,this article proposes that setting the valve after the valve and the pump can achieve the purpose of slowing down the water hammer.