| Nuclear energy is a safe,clean energy that can be used on a large scale.The development of nuclear energy plays a vital role in safeguarding national sovereignty,protecting the ecological environment,and promoting scientific and technological progress.Benefiting from the advantages of lead-Bismuth Eutectic(LBE)with good heat transfer performance,high boiling point,and low chemical activity,Lead-cooled Fast Reactor(LFR)was selected as one of the fourth-generation reactor systems and the reactor type of the China initiative Accelerator-Driven System(Ci ADS).The flow characteristics of the fuel assembly have a significant impact on the safety and economy of the reactor systems.Wire-wrap spacers are usually used as positioning components of fuel bundles in liquid metal-cooled fast reactors,so it is necessary to study the flow characteristics in the fuel bundle channel.However,there are some problems such as high cost,great difficulty,and high risk to carry out an experiment with LBE.Therefore,this dissertation studied the flow characteristics of the wire-wrapped fuel bundle channel based on the similarity theory,combined with experimental measurement and numerical simulation methods.In this dissertation,a Visual Hydraulic Experimenta L Platform(VHELP)was designed and built,a 19-pin wire-wrapped fuel assembly model was produced using polymethyl methacrylate,and the following work has been carried out:(1)Eighteen axial differential pressures and twelve traversal differential pressures in edge subchannels with Reynolds numbers in the range of 3750 to 16250 were measured with differential pressure sensors,using deionized water as the working liquid.The results show that the pressure distribution is uneven,and there are obvious highpressure and low-pressure zones.The axial pressure fluctuates and decreases along the flow direction,and the fluctuation period is one pitch(H).When the axial height increases by 1/6H,the transversal pressure distribution changes by 60° along the direction of the wire-wrap spacer,and the change period is 1H.Rehme and Cheng and Todreas Detailed(CTD)models have the smallest error with the experimental data when predicting the relationship between the friction coefficient and Reynolds numbers.The critical Reynolds number of the transitional flow and turbulent flow is about 11700,and the deviation from the value predicted by the CTD model is 8.33%.(2)Particle image velocimetry(PIV)was employed to measure the velocity distribution in the XZ plane and YZ plane of the wire-wrapped fuel bundle channel,and sodium iodide solution was used as the refractive index matching(RIM)liquid.It was found that both the axial and transversal variation periodicity of the velocity distribution was 1H.As the Reynolds number increases,the shape of the velocity distribution does not change and the value increases proportionally;the root mean square transversal velocity increases proportionally;the value of the normalized transversal velocity does not change,the maximum value is about 40%,and the peak appears at a position behind3/4H.The transversal velocity changes as a cosine function with the increase of the Zaxis coordinate,and the cross-flow near the wire-wrap spacers becomes stronger,and the velocity direction is deflected.(3)The software Fluent was used to simulate the flow characteristics of the fuel bundle channel,and the simulation results were compared with the experimental data.It was found that the Reynolds Averaged Navier Stokes(RANS)turbulence models can accurately simulate the flow characteristics of the wire-wrapped fuel bundle channel.The calculation result of the SST k-? model has the smallest deviation from the experimental data.(4)A visual fuel bundle manufacturing and cleaning technology was developed,and various RIM solutions and their advantages and disadvantages were summarized.At the same time,a new type of RIM solution of 72.2 vol% tetralin-27.8 vol% absolute ethanol was mixed,and a working fluid physical property measurement and purification experimental platform was built to explore the formulating principle of RIM solutions and the relationship between Reynolds numbers and the concentration and temperature change.The study found that the Newton equation has the smallest deviation from the experimental measurement data when predicting the mixed solution’s refractive index.The Reynolds number is sensitive to temperature,so it is necessary to set up a heat exchange device in the experimental loop to control the working liquid’s temperature and seal the loop well.This study further enriches the database of the flow characteristics of the wirewrapped fuel bundle channel,which can provide data support for the design and operation of the fuel assembly in Ci ADS.At the same time,the relevant experience in this dissertation is helpful to the development of visual hydraulic experimental technology in the future. |
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