Coupled Numerical Simulation On The Flow And Heat Transfer Process And The Multiple Stresses Of Tube In A Steam Generator

In the pressurized water reactor(PWR)nuclear power plant,a steam generator is the hub device between the primary side and the secondary side.The safe and efficient operation of the steam generator is essential for the nuclear power plant.The tubes of steam generator bear various stresses during the flow and heat transfer process,which is prone to stress corrosion and wear,and thus undermines the tube integrity.Therefore,the study on both the heat transfer and fluid flow and the steam generator tube stresses at the effect of fluids is significant to reveal the reason of heat transfer tubes degraded failure and for optimization of steam generator structure design.Refer to the actual operating parameters and the steam generator structure of Daya Wan Nuclear Power Plant,A simplified physical model of the U tube heat transfer region was established.The steam generator flow and heat transfer processes from 100%-50% working conditions were numerically investigated using CFX software.The distributions of key thermal parameters of steady-state operation were revealed,as well as the parameter dynamic variations during the down load process.The temperature and pressure loads of the CFD result at rated condition were transferred to structural model in the Workbench platform.A steady-state thermal analysis and a structural static analysis were carried out,and the stress distributions of the tube and support plates were revealed.The results are as follows.Corresponding to 100%,70% and 50%conditions,the primary-side fluid outlet temperature were 297.2 ?,295.6 ? and 294.8 ?,and the average export steam quality of secondary side was 24.5%,16.7% and 12.1%,respectively.The simulation results are consistent with the actual parameters at corresponding condition of Daya Bay Nuclear Power.During down load process,The heat intensity both the primary and secondary sides decrease,the fluid thermal parameter values reduce with time and the disturbance of the support plate on the secondary side fluid is also waning.Along the tube length,the tube thermal stress changes in a fashion similar to the change of tube temperature difference,with the stress concentrations occurring at the TSPs.The average mechanical stress of the tube relates to the medial and lateral hydrostatic pressure difference,and fluctuates in the bend region of the U tube.The inner wall thermal stress is 47.7 MPa at thecontact position between the hot leg tube and the tube sheet,the average mechanical stress of the inner wall at TSPs is about 86 MPa and the average mechanical stress of the outer wall at TSPs is about 75 MPa.The stress calculation results are all consistent with actual measured values.Under the combined loads of temperature and hydrostatic pressure,the coupled stress is the combined effect of the thermal and mechanical stresses.The coupled stress of the outer wall is a superposition of the thermal and mechanical stresses.On the other hand,the thermal stress and the mechanical stress counteract each other in the inner wall at locations of the tube away from the TSPs.At the TSPs,the change in coupled stress concentration is similar to that of the thermal stress.In the bend region,the change in coupled stress is essentially the same as that of the mechanical stress.The thermal stress,mechanical stress and coupled stress of the tube are exhibit a periodicity in the circumferential direction at the TSPs,while the radial stresses of the tube are uneven at the contact sites and middle portions of the water holes.Under long-term thermal and hydrostatic pressure loads,the tube is prone to stress corrosion and high cycle fatigue at TSPs.