Research On Binocular Vision Detection System Of Fuel Assembly Deformation Based On Underwater Radiation Tolerant Camera

As the core component of nuclear power system,the fuel assembly can produce energy.There exist several influence factors for the fuel assembly,such as assembly stress,thermal stress and radiation growth,and so on.They could lead to local deformation of fuel assembly during the working process,installation difficulty,and assembly damage acceleration,and so on.So the fuel assembly deformation state is important monitoring index in the process of the core operation.However,due to the high radioactivity of the measured target,at present,most measurement methods of fuel components adopt contact measurement,which has the problems of less measurement parameters and easy activation of equipment.The measurement method based on underwater binocular vision,as a research focus of non-contact measurement,can realize non-contact,multi-parameters and efficient measurement of large-scale fuel assembly(about 4000 mm length).Under the condition of the special underwater nuclear radiation environment,the signal-to-noise ratio and working stability of ordinary underwater camera unit applied in binocular module are seriously affected.Meanwhile,high radioactivity also leads to poor uniformity of temperature field in water environment,and affects the accuracy and stability of underwater binocular measurement module.Therefore,this paper studies the key technology of the fuel assembly deformation detection system based on underwater binocular vision.The main research contents and achievements are as follows:(1)According to the radiation environment of the application site,a suitable nuclear radiation test is designed.Through the analysis of image sensor structure and process,the image sensor that meets the application requirements is selected,and the detailed structure design of the underwater camera module is given based on the CMOS image sensor.The application rule of the camera module is obtained by the single frame analysis of gray value and image histogram and the continuous analysis based on image SNR of the collecting irradiated images.The measurement methods of various target parameters are introduced in detail.Based on the calibration method of the regional block and calibration target,the internal and external parameters of the underwater binocular camera are calibrated.And the distortion correction results are given.By means of Harris feature point and regional grayscale cross correlation method,the fast stereo matching of binocular camera is realized under the noise interference of nuclear radiation,and the method of calculating 3D coordinates is given.(2)The radiation of the fuel assembly can seriously reduce the signal-to-noise ratio of the camera unit of the deformation detection system.Through the design of the radiation test and the noise analysis of acquisition images,a model based on mixed Pulse-Gaussian noise is proposed for radiation noise.At the same time,based on the joint processing of ROAD filter and NLDD filter,the radiation noise is effectively suppressed.In the deformation measurement of large fuel assembly,due to the fixed structure of the detection equipment,the deformation of the target relative to the detection equipment has a cumulative effect.And the local or global defocusing blurring caused by excessive deformation will inevitably occur.A clarity evaluation function of defocus stateis provided.According to the estimation of the defocus radius and the calculation of the image SNR,an efficient and reliable module of fuzzy image restoration based on wiener filtering is realized.The test for the focal and aperture parameters of the optical system of the detection equipment is designed,and the precision of the binocular measurement module is analyzed.(3)The high radioactivity of the fuel assembly makes it self-heating,which will lead to the poor uniformity of temperature field in the working water environment.And the images captured by camera unit will produce edge random distortion,details lost and blurry.Through the analysis of the factors such as temperature and the refractive index of water environment,the mechanism of the thermal disturbance is determined.Based on the thermal disturbance simulation test platform and test module,the level of distortion of target image in radial and axial directions is evaluated through using the gray scale distribution,structural similarity image measurement and normalized maximum gray-scale gradient definition evaluation function of underwater images.(4)According to the large-size feature of underwater detection target,a deformation detection system for underwater large fuel assembly based on multiple sets of binocular vision module is proposed,which is composed of underwater binocular array acquisition subsystem and parameter 3D measurement subsystem.The hardware overall framework of the acquisition subsystem is given.Especially,the parameter control of the camera module and the drive circuit of miniaturized motor unit are introduced in details.At the same time,according to the software requirements of the system,the overall framework and interface of the software system are designed.Finally,through the measurement experiment of simulated pool and nuclear industry field,it is proved that the system's ability to local parameter measurement meets the demand of field application.And the measurement precision of local parameter can reach 0.2 mm.