Research On Modeling And Simulation Of Helical Coil Tube Type Once-through Steam Generator

Due to its compact structure,high heat transfer coefficient and compensation for thermal expansion,the helical coil tube type once-through steam generators(HCSG)have been utilized in various reactors,especially in integral type reactors.A thermal-hydraulic model for HCSG is developed to analyze its operational characteristic accurately.The model adopts the one-dimensional four-equation drift-flux model for two-phase flow.The heat transfer regions inside the tubes are divided into three segments: economizer,evaporator and superheater region respectively;the fully developed subcooled nucleate boiling and the mist evaporation region are also taken into account;then,proper heat transfer coefficients and friction factors correlations for helical coil tube are employed according to the boiling region.The governing equations are discretized by the fully conservative implicit finite difference and second-order upwind scheme on the staggered grid.For single-phase regions,the nonlinear equations are simplified into a nonlinear equation about density and solved by the secant method.For two-phase regions,the governing equations are simplified into nonlinear equations about pressure,void fraction and enthalpy,then solved by the modified Newton method.The Thermal Hydraulic performance analysis code of helical coil Once-Through Steam Generator(TH-OTSG)is programmed by C# and evaluated according to the data of the HCSG of the International Reactor Innovative and Secure(IRIS)at steady and transit state.The comparison shows that the steady state results of the new model at full power correspond with the design parameters and the literature references well.Based on the IRIS control requirements,specifying constant average coolant temperature across the core at constant steam pressure,the distributions of parameters such as pressure and temperature are predicted from 100%FP to 20%FP using 20%FP as step,respectively.Then,the dynamic simulation considers the changes of the feed water flow rate and temperature,the hot leg flow rate and temperature,the steam pressure with ±10% step change,individually.The results justifiable according to the qualitative analysis of HCSG and agree with those of RELAP5 on the whole.The validated results demonstrate that TH-OTSG can provide reasonable prediction on the operational thermal-hydraulic responses of HCSG and serve as reference for the design of HCSG control systems.