Research On Dynamic Performance Of Once Through Steam Generator Based On Implicit Scheme

In the pressurized water reactor of nuclear power plant,because the once through steam generator is more compact and modular than the traditional natural circulation steam generator,it can bring better heat transfer effect and design economy.The once through steam generator is connected with two circuits.The primary side fluid not only has high temperature and pressure,but also carries radioactive substances.There is a two-phase flow state in the secondary side fluid during heat exchange,and the heat transfer deterioration will occur when the liquid film evaporates dry.Therefore,the working environment of the steam generator is relatively bad,which poses a great threat to the safety and reliability of the nuclear power system,It is necessary to study and analyze the working performance of steam generator.Based on the calculation of thermal hydraulic parameters,the heat exchanger tubes are divided into different heat transfer zones based on the two simultaneous interpreting of the fluid flow and heat transfer characteristics of the B&W based steam generator.Under the assumption of simplification,the one-dimensional homogeneous flow mathematical model of the once through steam generator is established by three conservation equations,and the implicit difference scheme is used to discretization the equations.At the same time,the relevant model of scaling process is given,and the working performance simulation source program of once through steam generator is developed to simulate the working performance of once through steam generator under normal working condition,fault working condition and scaling.The results show that under normal steady-state working conditions,the outer wall temperature of the heat transfer tube rises by about 19 ℃,and the outlet pressure of the secondary side is about 6.36 MPa.After reducing the power,the temperature difference of the primary side flow decreases,the outlet pressure of the secondary side increases,and the length of the boiling section shortens.However,changing the working conditions can not curb the deterioration of heat transfer,and the soaring range of the wall temperature of the heat transfer tube is almost unchanged.In the process of dynamic variable working conditions,the outlet temperature of the primary side is stable in about 80 s from 100% variable working conditions to 90%,while the time from 100% variable working conditions to 70% stability is about 100 s.When the fluid inlet flow at the secondary side increases by 20%,the outlet temperature at both sides decreases by 4.2 ℃ and 13 ℃ respectively,and the outlet pressure at the secondary side decreases by 0.018mpa;In the small break accident of heat transfer tube,the fluid outlet temperature on both sides produced fluctuation response,which decreased by about 1.4 ℃ and 0.7 ℃ respectively after stabilization.In the process of scaling,the initial stage of heat transfer tube scaling plays a role in strengthening heat transfer to a certain extent,and the outlet temperature of the secondary side fluid increases slightly by 0.5 ℃;When the dirt reaches a certain thickness,the heat transfer process is weakened,and the fluid outlet temperature at the secondary side decreases by 1.1 ℃.