Research On Fiber Optic Pressure/Strain Sensing System For Thermo-hydraulic Experiment Of Fuel Assembly

The thermal-hydraulic test of fuel assembly is to study the performance of the internal components of fuel assembly by simulating the normal working environment of nuclear reactor.It is a key link in the field of nuclear safety verification and a prerequisite for the normal operation of nuclear reactor.Because the fuel assembly is under the scour of high temperature,high pressure and high speed coolant flow(350℃,20MPa),vibration fatigue occurs in the internal components of the fuel assembly.Pulse pressure and strain on the surface of the fuel assembly is to analyze the two key parameters of the component vibration fatigue,therefore,fluctuating pressure and strain of the measurement to get fuel components internals,prediction of mechanical deformation components internals of use fixed number of year,improve the processing technology and structure of the component design has very important significance.In this thesis,a sensing system of pulsation pressure and strain based on Fabry-Perot optical fiber is established to measure the pulsation pressure and strain of fuel assembly.Based on Fapot multi-beam interference and non-scanning correlation theory,and according to the processing technology and fixation mode of silicon diaphragm,an optical-mechanical coupling model of diaphragm type fiber pulsating pressure sensor was established.The influence of parameters such as range,sensitivity and resolution of the pulsating pressure sensor and the thermal deformation of the diaphragm on the sensor performance was analyzed.The strain transfer model and the optical-mechanical coupling model of the fiber optic strain sensor are established,the transmission characteristics of the strain sensor are analyzed,and a new strain transfer structure is designed.On the basis of the previous work of the research group,the performance test of the pulsating pressure sensor,the processing of the transmission structure of the strain sensor and the manufacture of the sensor were completed,and the performance test of the strain sensor was carried out.Based on the analysis of the output electrical signal characteristics and noise characteristics of the demodulation system,the related hardware signal processing circuit and data processing algorithm are completed to improve the signal to noise ratio,stability and precision.The pulsating pressure and strain of fuel assembly were measured under thermal-hydraulic test conditions.The performance test of the sensor shows that the measuring range of the pulsating pressure sensor is up to 4.1MPa,the sensitivity is up to 1.62nm/k Pa,the theoretical measuring range of the strain sensor is up to 2800με,the theoretical sensitivity is up to13.3nm/με,and the demodulation rate of the demodulation system is up to 5k Hz.The sensor system is used to measure the pulsating pressure and strain of the fuel assembly in the thermal-hydraulic experiment.The experimental results show that the sensitivity of the pulsating pressure sensor and the strain sensor are up to 1.66nm/k Pa and 12.6nm/μεwhen the temperature is 200℃ and the thermal-hydraulic experiment condition.The sensor system can effectively measure the pulsating pressure and strain of the fuel assembly in the thermo-hydraulic experiment.