Analysis Of Thermal Stratification In PWR Surge Line

Thermal stratification is phenomenon which occurs when fluids of different temperatures co-exist in the same structure.In the PWR surge line,one end is connected to with a low temperature and high-speed coolant flow while other end is connected to the high temperature pressurizer regulator.During normal operation and start-up of the reactor,turbulent flow will occur,and thermal stratification will also form in the wave tube.That is,high-temperature and low-density fluid is in the upper part,and low-temperature and high-density fluid is in the lower part,and the pipeline will generate thermal stress.In addition,the temperature oscillation phenomenon will occur at the interface of hot and cold fluids,and the pipeline will produce fatigue damage for a long time.Therefore,it is necessary to study the thermal stratification of the PWR surge line.In this paper thermal stratification phenomenon of the third-generation pressurized water reactor(AP1000 PWR)surge line is analysed using CFD software(ANSYS FLUENT)with large eddy current(LES)model.First several meshing models of surge line are designed in ICEM software and mesh size is determined by sensitivity analysis and their performance is tested for a transient analysis.The mesh which is least sensitive to change is chosen.Secondly,the spatial and temporal distributions of the velocity and temperature in surge line are analysed under the specific inlet velocity.The results showed that AP1000 PWR surge line has less difference in temperature and for the short period of times at corresponding areas.It was also observed that thermal stratification is highest at the start of the horizontal part of the surge line and then weakens with the flow direction.Thirdly,the influence of different inlet flow rates on the thermal stratification distribution characteristics is analysed.In the results,it was observed that thermal stratification phenomenon becomes more serious with the larger fluctuating inlet velocity.Finally,the thermal stratification characteristics of the second-generation PWR surge line and the third-generation AP1000 surge line are compared and analysed.Results showed that compared with the surge line in the traditional PWR,the AP1000 pressurizer surge line has a lower thermal stratified temperature difference and shorter thermal stratification appearance time.