| The lead-cooled fast reactor(LFR)is one of the six fourth-generation reactors,which has advantages such as good safety,excellent economy,small volume,and less nuclear waste,and has broad application prospects.The China Initiative Accelerator Driven System(Ci ADS)being built by the Institute of Modern Physics,Chinese Academy of Sciences,during the 12 th Five-Year Plan,adopts a lead-bismuth fast reactor as a burner for spent fuel.As an advanced reactor that uses a new type of coolant,the measurement of liquid lead-bismuth flow rate is one of the key issues in thermalhydraulic research and reactor operation monitoring.In the experimental research and operation of the lead-bismuth fast reactor,high-precision calibration of highly stable flow meters is needed to achieve accurate flow rate measurement.Since the development of domestic lead-bismuth flow meters started relatively late,there is currently no high-precision mature product of a lead-bismuth flow meter calibration device to serve the development and verification of flow meters in China.Therefore,the Institute of Modern Physics,Chinese Academy of Sciences,is promoting the design and construction of a lead-bismuth flow meter calibration device based on the static mass method.In order to achieve prior analysis and design optimization of the relative standard uncertainty of the lead-bismuth flow meter calibration device based on the static mass method,this paper first conducts theoretical analysis and numerical calculations on the key equipment of the calibration device,such as the reversing valve and the pressure regulator tank,and demonstrates the selection of the technical route and researches the operating characteristics of the equipment.Through the calculation of the closed reversing valve,it is found that water hammer will occur when the closed reversing valve operates in lead-bismuth medium,and the resulting water hammer wave will affect the flow stability of the flow meter in the pipeline and pose a threat to the safety of the device.Therefore,the closed reversing valve is not suitable for the lead-bismuth flow meter calibration device.For the open reversing valve scheme,the operating characteristics of the reversing valve under different flow rates and torque cylinder drives are studied using a CFD-based bidirectional coupling calculation method,and the B uncertainty component of the reversing valve and the relative system error of calibration under different timing methods and different speed distributions of the reversing valve nozzle outlet are obtained using the travel difference method.The analysis of the open reversing valve shows that the greater the cylinder thrust,the smaller the B uncertainty of the reversing valve;when the reversing valve baffle is moved to the midpoint of the stroke as the timing time,the relative system error introduced by the reversing valve is lowest;the magnitude of the B uncertainty of the reversing valve can reflect the envelope value of the relative system error introduced by the reversing valve using different timing times.For the pressure regulator tank,the compression characteristics of the gas chamber and the effect of smoothing pressure fluctuations are analyzed based on the ideal gas equation,and the operating characteristics are detailedly simulated using the CFD method.The analysis shows that the pressure regulator tank in the device meets the performance requirements,and the results of theoretical analysis and CFD analysis mutually verify the reliability of the calculation results.Then,by adding virtual lead-bismuth gas phase properties to the RELAP5 MOD4.0program,this article solves the problem of the program’s inability to simulate the contact between lead-bismuth and non-condensing gas conditions,enabling it to simulate the dynamic behavior of gas-containing vessels in calibration devices.The improved program was validated using CFD simulations of a pressure-stabilizing tank,which showed that the improved program has good applicability,reliability,and robustness.Based on the improved RELAP5 MOD4.0 program,a model of a lead-bismuth flowmeter calibration device was established to analyze the dynamic characteristics of the device,and the following conclusions were drawn: the pump in the lead-bismuth flowmeter calibration device introduces high-frequency pressure pulsation,and the pressure-stabilizing tank effectively filters out high-frequency oscillations.When the fluctuation amplitude of the inflow rate to the pressure-stabilizing tank is around 2.5%,there is no significant fluctuation in the outflow rate of the pressure-stabilizing tank.During the calibration process,the introduction of lead-bismuth into the weighing tank causes a decrease in the storage tank level and a decrease in the tank pressure,resulting in a decrease in the calibration loop flow rate.However,this problem can be solved by adjusting the pump frequency.Choosing appropriate control parameters to adjust the pump speed can ensure that the calibration device has good flow stability during calibration.Finally,based on the instrument’s dynamic response characteristics,a virtual flowmeter system was established,and a framework and calculation process for prior analysis of the relative uncertainty of static mass flowmeter calibration devices were established using the lead-bismuth flowmeter calibration device’s numerical analysis model and the GUM and MCMs.The uncertainty analysis of the lead-bismuth flowmeter calibration device was completed.The calculation results showed that,within the scope of this study,the uncertainty of the lead-bismuth flowmeter calibration device based on the static mass method at the maximum flow rate satisfies the design indicators.When the flow stability of the calibration device changes,the uncertainty of the device obtained using the MCM also changes,with greater uncertainty for devices with poor flow stability.However,the GUM cannot capture this feature,which is a limitation of the GUM in theory and practice.The uncertainty of the calibration device obtained using the GUM is relatively conservative compared to that obtained using the MCM,but the GUM is simpler to calculate.This article preliminarily establishes the process for uncertainty analysis of calibration devices based on a full-system numerical analysis model and the MCM.The MCM is theoretically more complete and may have higher computational accuracy,and it is worth further research to establish a theoretical system and operating guidelines for uncertainty assessment of calibration devices using the MCM. |
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