Study On The Impact Location Estimation Of Loose Parts In Nuclear Power Plant

Based on the High Technology Research and Development Program of China "Research on the Key Technology of Loose Part Monitoring in Nuclear Power Plant (No.2007AA04Z426)", loose parts'impact signal preprocessing and identification and impact localization methods of loose parts are studied.In chapter one:The importance and background of setting Loose Part Monitoring System (LPMS) in Nuclear Power Plants (NPPs) are expounded. Introduced the key technology, system structure and develop progress of LPMS. The impact localization methods now available are summarized. Finally, the study background and overall frame of the dissertation are given.In chapter two:a signal preprocessing and impact signal identification method is proposed by analyzing the noise signal of NPP and impact signal of loose parts. The signal is whitened using adaptive AR model, and then the SNR of signal can be improved. Extract the Linear Predictive Coefficients (LPC) of the whitened signal as its characteristic, and then using Supporter Vector Machine (SVM) to identify whether the recorded signal contains impact signal. Simulation and experiment results show that the method can identify the signal in low SNR.In chapter three:The time arrival difference error and wave speed measurement error influence on the positioning accuracy of triangle positioning method are studied. A loose part positioning method based on Ensemble Empirical Mode Decomposition (EEMD) and Hilbert Transform was proposed. The method uses EEMD to decompose the signal into some singal vibration mode, and then calculate the envelope of the main vibration mode using Hilbert Transform, find the first peak of the envelope as the arrival time of signal. According the arrival time and wave propagating velocity, the location of loose part can be estimated. Experiment results show that the method can estimate the location of loose part fast and accurately.In chapter four:Improved the circle intersection positioning method to get the position of loose part. A wave propagation distance estimation method based on time-frequency analysis is studied, and then a loose part positioning method based on smoothing pseudo D-Flandrin distribution is proposed. Through the analysis of the dispersive characteristic of bending wave, build the relationship between the group delay and the frequency of wave, and then find that the D-Flandrin distribution is a suitable time-frequency analyzing method for bending wave in plate. After the time-frequency analysis, the Non-linear Least Square Method are taken to estimate the distance between impact point and sensors, then the position of loose part can be estimated using circle intersection positioning method. Experimental results prove the validity of the method.In chapter five:The positioning method in cylindrical shell and spherical shell is studied. It's hard to positioning the loose part in cylindrical shell as wave axial and circumferential propagation velocity is different. An improved scan positioning method is proposed based on the analysis of impact signal's propagation model in cylindrical shell. This method estimates the position of loose part by calculate the axial velocity, circumferential velocity, and the initial collision time. The particle swarm optimization algorithm is applied to accelerate scanning speed, which can greatly save search time. Experimental results show the effectiveness of the proposed method.In chapter six:Based on the theory study, a nuclear loose part monitoring system protype is developed using Lab VIEW. Detailed analysis of the system architecture and main modules are taken, and the software module structure and system interfaces are designed, online monitoring, location analysis and other functions are achieved, and the system is simulated on plate.In chapter seven:The main content of the dissertation research is summarized, and the prospect of loose part monitoring research is presented.