Study On Flow Measurement Method For In-situ Calibration Of Permanent Magnet Sodium Flowmeter With Embedded Vortex Generator

Liquid metal sodium,as the coolant of sodium cooled fast reactor,has the advantages of small neutron absorption cross section and large specific heat capacity,but its chemical properties are active.Therefore,in order to ensure the safe operation of sodium cooled fast reactor,it is necessary to accurately monitor the sodium flow in the cooling system.Permanent magnet sodium flowmeter is often used in sodium flow measurement,but its permanent magnet will be affected by high temperature and radiation at work,demagnetization phenomenon,resulting in the increase of sodium flow measurement error.To do this,it needs to be calibrated regularly.Since the inner submersible sodium flowmeter needs to be immersed in the sodium solution at work and cannot be taken out,therefore,for this kind of flowmeter can only be calibrated in situ.The flow measurement method based on cross correlation analysis is improved,and the accuracy of flow measurement is improved.According to the characteristics of the output signal of the sensor and the requirements of the verification regulation,the sodium flow measurement method based on the cross-correlation analysis was improved from three aspects of signal filtering frequency band,cross-correlation points and fitting method,which effectively suppressed the noise interference and reduced the error of the indication value.The experimental data processing results show that: for the sensor with diameter of 40 mm,the measurement accuracy is improved to level 1;for sensors with a caliber of 65 mm,the measurement accuracy is increased to level 2.The adaptive filter modeling method is applied to the signal processing of the actual sodium flow sensor for the first time,and the accuracy of flow measurement is further mentioned.Considering the actual signal characteristics and the convergence speed of the algorithm,the parameters and iteration mode of the data processing algorithm are selected and optimized to reduce the delay estimation error.The comparison of the data processing results of the three methods shows that,in general,the measurement error and repeatability error of the adaptive filtering modeling method are small.The problem of measurement lower limit of in situ calibration method is firstly studied and the main reason of limited measurement lower limit is determined.According to the collected experimental data,the lower limit of measurement is determined.The uncertainty of data processing results was calculated.The reason of limiting the measurement lower limit is analyzed qualitatively,and the signal to noise ratio(SNR)characteristic factors of the sensor system are defined and calculated.Through theoretical analysis and verification experiments,it is confirmed that the insitu calibration accuracy and the modified model are not affected by temperature.Based on the mechanism of sensor signal generation,the influence of temperature is analyzed theoretically.On this basis,the experimental data of the sensor at 360℃ and 250℃ were processed.The results show that the temperature does not affect the accuracy of in-situ calibration and the modified model,which is in accordance with the theoretical analysis.