Analysis of Tube Flow Field and Flow-Induced Vibration of HL-T67 Steam Generator

The steam generator of the pressurized water reactor nuclear power plant is the hub of the primary circuit and the secondary circuit. The fluid induced vibration of the heat exchange tube causes the fretting wear between the heat exchange tube and the supporting structural components, causing local damage of the heat exchange tube. The continuous fretting wear will lead to the further initiation and expansion of the wear surface crack of the heat exchange tube, and even lead to the failure of the heat exchange tube. Revealing the fretting wear characteristics of steam generator heat exchange tubes provides theoretical support for maintaining the safe and stable operation of nuclear power plants. In this paper, the self-designed fretting wear experimental device was applied. The electromagnetic vibration exciters were used to simulate the fluid induced vibration of the steam generator heat exchange tube. The excitation response and fretting wear behavior between the steam generator heat exchange tube and the trefoil broach support structure at room temperature air dry and room temperature water environment were studied. It was found that the heat transfer tube is a combined motion mode of impact-slip in the support structure. And the equation of motion of the heat exchange tube in the support structure was derived, and the theoretical model of the movement of the heat exchange tube in the support structure was established. The influence of factors such as dimensionless support clearance, preload, offset position, excitation force ratio and support ratio in the support structure on fretting wear behavior was studied by measuring the contact rate, contact force, friction coefficient, work rate, wear surface hardness, wear scar morphology, wear scar element composition, wear scar profile, wear volume, wear coefficient of the heat exchange tube and other indicators. With the increase of the dimensionless clearance between the heat exchange tube and the support structure, the contact rate and the contact force were negatively correlated. When the dimensionless clearance was small, the work rate was positively correlated with it, while the dimensionless clearance was large, the opposite was true. The preload mainly affected the slip distance by affecting the friction coefficient, and finally affects the work rate. The contact rate, contact force and work rate were positively correlated with the ratio of the excitation force in the orthogonal direction. The support ratio had an effect on the motion mode of the heat exchange tube. When the support ratio was low, the impact movement of the heat exchange tube was dominant. Otherwise, the slip motion was dominant. The influence of the water environment was mainly to wash the abrasive layer and reduce the friction coefficient, and the damping effect of water on the heat exchange tube was obviously enhanced when the exciting force was small. The wear surface of the heat exchange tube appeared to be hardened during the fretting wear process. The wear mechanism was abrasive wear, delamination and oxidative wear, and furrows and exfoliation pits were found on the worn surface, and material transfer occurred. As the wear time increased, the oxidation increased and the wear was intensified. Under the long-term wear, the trefoil broach support structure with a support ratio of 0.25 had the largest wear coefficient.