Study On Fluctuating Pressure Monitoring Sensor System Within Pressurized Water Reactor

The safety issue is one of the most significant problems in the development of nuclear power.The most important precondition of building a nuclear power plant is to ensure its safety.The structural integrity of core structure is an important factor to the safety of pressurized water reactor(PWR)nuclear power plants.The fluctuating pressure caused by the coolant flowing motion would lead to the dynamic stress in the core structure.With long term operation,the dynamic stress may cause fatigue damage in the structural component of reactor,and then induce the looseness,deformation and dropping out of fastenings.This serious problem would cause the unplanned shutdown of nuclear power plants and bring a major economic loss.The flow-induced vibration experiment is a necessary test in the design verification process of nuclear power plant.The condition monitoring of structural component in the reactor and the measurement of fluctuating pressure has vital function on analyzing the failed mechanism of structural component fatigue damage caused by fluctuating pressure,predicting the service life of structural component and optimizing the structural design.Due to the volume,the working temperature,performance and other problems,electric sensors could not meet the working environment of PWR which consists of high temperature,high pressure(350°C,15.5MPa)and complex electromagnetic interference.Compared with the electric sensors,the fiber F-P sensors have outstanding advantages due to their high precision,high stability and anti-electromagnetic interference.The multi-direction measurement of fluctuating pressure realized by changing the structure of F-P cavity is one of the most promising method to be used for the monitoring of fluctuating pressure in the reactor.In this paper,the fiber F-P fluctuating pressure sensing system was presented for measuring the fluctuating pressure of coolant in the reactor,which helps to ensure the condition monitoring of structural component in the PWR.The optics-machinery coupling model of diaphragm type F-P fluctuating pressure sensor based on non-scanning correlation demodulation method was built.According the built model,the deformation characteristic and frequency characteristic of sensing diaphragm was analyzed to build the bending deformation of fluctuating pressure sensor.The measurement range of F-P fluctuating pressure sensor was calculated by combining the largest deformation of sensing diaphragm before the failure of sensor optical performance and the largest deformation of sensing diaphragm before its plastic deformation.The mathematical relation between the pressure resolution of sensor and the optical resolution of demodulation system was built.The structural parameters of fluctuating pressure sensor was optimized.The fiber F-P fluctuating pressure sensor was fabricated with the studying the processing technology of F-P sensor.Based on the non-scanning correlation demodulation method,the demodulation system was designed.The peak moving average filter was proposed to enhance the demodulation precision.At last,the optical module of the demodulation system was calibrated,and then the performance of F-P fluctuating pressure sensor was tested.The results showed: As for the designed demodulation system,the optical resolution is 13.95 nm,effective measuring range is from 10.33?m to 32.39?m.As for the designed diaphragm type F-P fluctuating pressure sensor,the maximum static pressure is 5MPa,the dynamic pressure is ±200KPa,the theoretical pressure sensitivity and the theoretical temperature sensitivity are respectively 2.54nm/KPa and 0.95nm/°C.After the experimental test,the pressure sensitivity at normal temperature is 4.18nm/KPa,the pressure sensitivity at 350°C condition is 3.21nm/KPa,and the temperature sensitivity is 4.63nm/°C.After all,the designed system can satisfy the fluctuating pressure monitoring within PWR,thus providing an effective monitoring method for structural component.