| Fiber Bragg grating has the advantages of wavelength modulation,absolute measurement,anti light intensity disturbance,no electromagnetic interference and so on.Among them,fiber Bragg grating(FBG)is the most mature type.At present,with the advantages of mature production technology,low production cost and excellent performance,fiber Bragg grating has been widely used in the monitoring of large-scale projects such as electric power,bridges,aviation,aerospace and ships.This paper mainly focuses on the monitoring of nuclear fuel reactor.As an industry with a high risk factor,the loss and consequences caused by safety accidents are incalculable.At present,a large number of traditional electrical sensors are mainly used in nuclear reactor monitoring;Detection of substances outside the reactor and computer modeling and simulation.These methods have certain limitations,and the use of fiber Bragg grating to monitor the key parameters in the nuclear reactor can effectively solve the disadvantages of various monitoring methods.In this paper,a simulated nuclear reactor system is built,and the fiber Bragg grating sensing technology is applied to the simultaneous monitoring of temperature,strain and vibration of fuel rods.The specific research contents include:(1)The basic sensing principle of FBG,the current research and application status of fiber Bragg grating are introduced.At the same time,the principle and application of several common nuclear reactor monitoring technologies are also introduced.(2)The method of simultaneous detection of temperature and strain parameters of fuel rod by FBG is studied.The strain sensitivity coefficients of the two bare fiber gratings are 0.875pm/με And 0.87pm/μεrespectively。Then,the packaging experiment is carried out on the double grating.One of the double FBGs is encapsulated on the strain gauge to make it sensitive to the effects of strain and temperature at the same time.The other FBG is fixed on the fuel rod through the capillary tube with a certain bending allowance.Their temperature coefficients are calibrated,which are 14.71pm/ ℃ and12.21pm/℃ respectively.In this package,the FBG fixed in the capillary tube is not subject to strain,and the temperature sensitivity decreases slightly.The FBG encapsulated by the strain gauge is affected by the two parameters of temperature and strain at the same time,and the double FBG temperature and strain coefficients are different.Therefore,the temperature strain decoupling equation can be brought into to solve the temperature and strain.The experimental results show that the maximum error of the temperature measurement of the sensor is ±1.4℃ and the average error is ±0.74℃.The sensing strain has a certain strain loss,which is 0-3000μεafter strain compensation In the sensing range,the strain variation trend is basically consistent with the theoretical value,and the maximum error of the sensor strain measurement is ±75.11με,The average error is±23.68με,It can be used as strain sensor.(3)FBG based fuel rod vibration detection experiment.The vibration calibrator applies the vibration signal to the fuel rod and observes the change of FBG central wavelength.The change of FBG central wavelength can stably reflect the change law of the vibration signal,and the first-order response frequency of the time-domain signal is obtained through the Fourier spectrum of the collected time-domain signal,which is basically consistent with the signal input by the vibration calibrator.Through the research of amplitude frequency response and acceleration response,the sensor can maintain flat and linear response at different frequencies and different response intensities.The amplitude frequency response and acceleration response prove the accuracy and reliability of vibration signal sensing by fiber Bragg grating combined with fuel rod.(4)The supporting host computer software of fuel rod multi parameter detection system based on Fiber Bragg grating technology is developed by using Lab VIEW platform.The UDP network protocol is used to collect the data stream sent by the fiber Bragg grating demodulator.The data receiving frequency is 1KHz,which is consistent with the transmission rate of the demodulator.The grating wavelength data is intercepted from the data stream and converted into decimal wavelength data.The calibrated temperature and strain sensitivity values are brought into the FBG temperature strain decoupling formula to calculate the temperature and strain parameters.To monitor the vibration signal,it is necessary to transform the spectrum of the array.At the software interface,through the real-time receiving and processing of the data,the waveform diagrams such as wavelength data,temperature,strain and spectrum are displayed at the same time,and the data can be exported to excel file for storage.(5)Build a test system to simulate the working environment of the nuclear reactor,simulate the reactor coolant,make a metal water tank,and encapsulate the fuel rod in the water tank to make the sensor work in the liquid environment.Reseal the dual FBG sensor to keep the sensor in a closed state for temperature,strain and vibration monitoring experiments.The results show that the sensor still has good performance in liquid environment.In the high temperature working area of 100-200℃,the maximum error of temperature measurement of the sensor is ±0.84℃,and the average error is about ±0.56 ℃.The packaging mode of strain sensor is improved from metal sheet pasting to direct embedding,which overcomes the loss of strain transmission.After strain compensation,0-2600με The maximum measurement error of the sensor is ±20.35με,The average error is ±8.81με,The sensing accuracy is further improved.,The sensing accuracy was further improved.The vibration response of the experiment is smaller than that of the laboratory environment,but it can still judge the vibration response of different levels and the size of water flow from the spectrum.It has certain engineering application value,and the sensing sensitivity can be improved through later research. |
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