Study On Thermo-Fluid-Solid Coupling Of Passive Residual Heat Removal Heat Exchanger In Nuclear Power Plant

The residual heat removal system is a device used to remove the core’s radioactive decay heat and the sensible heat of the primary system in the event of an emergency shutdown of the reactor.The efficiency and reliability of its heat transfer performance are critical to the operation safety of the entire nuclear power plant.Therefore,it is necessary to calculate and study its operation process.The research object of this paper is the secondary-side passive residual heat removal heat exchanger.After the secondary-side steam enters the heat exchange tube after starting,the heat is transferred to the seawater outside the tube through the tube wall,and the wall condensation occurs,and the seawater outside the tube is subcooled boiling.During operation,the heat exchange system relies on gravity to drive the circulation of fluid,and uses the density difference between water with different temperature to drive the natural circulation outside the heat exchange tubes,reflecting the passive design.The current related research on heat exchanger rarely considers the coupled heat transfer between the fluid and tubes,and the effect of two types of heat transfer with phase change on the heat stress of tubes: condensation inside the tube and subcooled boiling outside the tube.The main research content of this paper is the three-dimensional simulation of the secondaryside passive heat removal heat exchanger and the thermal-fluid-structure coupling based on the temperature distribution of the tube in the simulation results.First,a mathematical model is established,where the wall condensation model and the RPI boiling model are selected for the phase changes on both sides of the tube wall,and the accuracy and applicability of the two models are verified.Then a CCL program is written to complete the input of relevant parameters and the calculation of the required results.Finally,the thermal stress is calculated by transferring the temperature load from the tube wall to the structure so as to realize the thermo fluid-solid coupling to the heat exchanger,and a numerical simulation method of thermo-fluidsolid coupling was explored.Through the study of the thermal-fluid-structure coupling of the secondary-side passive residual heat removal heat exchanger,the change rules of the vapor mass fraction,temperature,and enthalpy of the fluid in the tubes are obtained.This paper also gets the distribution of parameters such as the temperature of the outer seawater,the vapor volume fraction,and the speed,as well as the temperature and heat transfer coefficient of the tube wall during the coupled heat transfer process.Finally,the load transfer of the temperature of the tube wall to the structure was achieved.The thermal stress distribution of the heat exchange tube,and the changes of its circumferential and radial stress are also given.