Study On Flow-induced Vibration Of Control Rods In The Pressurized Water Reactor

Fluid-induced vibration is a frequent phenomenon in fluid engineering.In PWR nuclear power plants.accidents due to fluid-induced vibrations occur from time to time.The control rod assembly is the key component of the nuclear power plant and plays an important role in controlling the start-up and shutdown of the reactor and adjusting the reactivity,especially in the event of an emergency failure.The reactor control rod assembly has a slender structure,and flow-induced vibration is likely to occur under the scour of the core coolant.Flow-induced vibration may cause wear and deformation of the control rod,which affects the reliable fall of the control rod and threatens the safe operation of the nuclear power plant.Therefore,studying the flow-induced vibration behavior and characteristics of control rods,assessing the structural integrity and effectiveness of the flow-induced vibrations,is of great significance to the safe operation of nuclear power plants.A lot of research work has been done on the structure-induced flow-induced vibration at home and abroad,but less research has been conducted on the flow-induced vibration of control rods.Previously,the flow-induced vibration behavior of the control rods was usually calculated and analyzed.In their research,the flow behavior of the control rods was often reduced to the cylinder vibration under lateral flow erosion,and the envelope spectrum analysis was performed.However,due to the slender structure of the control rod,the flow field around it is more complex,so this simplification often has some differences with the actual situation.In addition,some scholars have carried out experimental research based on simplified models.Due to the limitation of scale,these experiments usually adopt a scale-down model,and the flow field also has a lot of simplifications.Therefore,there are also certain differences between experimental results and real-heap cases..Therefore,from an engineering point of view,it is necessary to more realistically obtain the flow-induced vibration behavior of the control rod in the case of real reactors.At the same time,it is also necessary to establish a more realistic experimental platform and evaluation method for controlling the evaluation of rod-induced vibration behavior.In summary,this study has important engineering value and significant academic value.In this study,firstly,based on extensive research on the research and development status of flow-induced vibration technology of control rods and key equipments in nuclear power plants at home and abroad,the PWR control rods are the main research object,relying on the national "large-scale advanced PWR nuclear power plant and high-temperature gas cooling."Heap nuclear power plant" science and technology major project funding,set up a full-scale control rod flow induced vibration test bench,and the use of local visualization design to solve the internal structure of the complex structure of the flow field and structural displacement difficult to measure the problem.On the experimental bench,the flow-induced vibration characteristics of the control rod in suspension and the influence of the flow hole in the lower part of the control rod on the flow induced vibration of the control rod were studied.Secondly,the development of numerical simulation program for control rod flow-induced vibration was carried out,The program contains a fluid force calculation module and a structural finite element solution module.The result of the fluid force calculation module can be automatically introduced into the structural limit solution module to solve the flow induced vibration parameters of the PWR control rod.Thirdly,aiming at the lack of a special excitation spectrum in the flow-induced vibration analysis of control rods,based on the in-depth study of the power spectral density theory and the normalization method,this paper develops a dimensionless fluid excitation force for control rods.Research on envelope spectrum.Finally,in view of the problem of rod drop delay and excessive vibration caused by control rod flow caused by the size of the hole of the guide cylinder,a new improvement scheme of setting the flow-blocking plate is proposed,and the numerical simulation calculation and analysis of the prototype and the improved scheme are carried out to evaluate the anti flow vibration effect of the improved designThe main results of this study are as follows:1.A set of full-scale PWR control rod flow-induced vibration test rigs has been established.Through the combination of numerical calculations and experimental measurements,the turbulence flow field consistency with real reactors has been verified.The gantry can carry out flow induced vibration engineering test on the PWR control rod,which solves the problem that the full-scale and true flow field test rig is lacking in the PWR control rod flow induced vibration test in China.2.In the numerical simulation and measurement experiments of the flow field around the control rod guide cylinder,it was found that the lower flow hole has a greater influence on the flow field around the control rod.The results of PIV measurement showed that the velocity and pressure of the fluid near the water flow hole are large,and the phenomenon of fluid mixing is obvious.This result is also consistent with the results of the previous numerical simulation.3.In the flow-induced vibration test of the control rod,the following conclusions were obtained:(1)When the lateral flow rate is less than 300 t/h,the control rod vibration is not obvious,and when the flow rate increases to 3 00t/h?500t/h The vibration of the control rod is obviously enhanced;(2)The experimentally measured displacement data show that the increase in lateral flow has a more severe effect on the vibration of the control rod relative to the change in the vibration displacement of the control rod caused by the longitudinal flow,and the lateral flow influences the control rod.The main factors of flow-induced vibration;(3)The empirical relationship between the maximum displacement of the control rod and the flow velocity of the surrounding fluid is proposed,which is of reference value for the application of the control rod to the flow-induced vibration engineering.4.Developed a control rod flow-induced vibration simulation program.By comparing the calculated results with the experimental results,the practicability of the program was verified.5.Based on the induction and processing of the experimental measurement results,a dimensionless fluid excitation force envelope spectrum dedicated to the control of the longitudinal flow is obtained for the control rod.The envelope spectrum can effectively reduce the general spectrum used in the current engineering design.Conservative,with a certain engineering application value.6.A new flow-blocking plate design scheme is put forward.Through the calculation and comparative analysis,it is concluded that eight groups of baffle design schemes can effectively reduce the overall lateral flow velocity in the control rod guide cylinder,which is only 20%-30%of the horizontal velocity of the prototype design scheme,which is conducive to reducing the vibration amplitude caused by the control rod flow.It may be an effective way to solve the imbalance between the resistance and the flow induced vibration of the control rod in the guide tube of PWR by adding a baffle near the flow hole of the control rod guide tube.