Automated girth weld inspection of nuclear fuel rods

Abstract

The girth welds joining the end plugs and the hollow tubes of nuclear fuel rods are inspected automatically using a technique that averages reflectance values, compares the reflectance values to standards defined as proportions of the average, and counts adjacent pixels outside the standards to analyze for defects exceeding a minimum defect size. The minimum defect size is checked by counting the adjacent pixels in mutually perpendicular directions, such as rows and columns in the collected matrix of pixel data. The maximum count in the two directions can be different, for profiling the maximum acceptable defect as to the direction of its extension relative to the tube and/or weld. Tubes are inspected prior to surface treatments that may conceal defects. The tube is fed, illuminated and rotated for at least one revolution at an inspection station, collecting line scans at regular angles synchronously with rotation using a line scan camera coupled to a digitizer to obtain the matrix of data encompassing the girth weld. A numerical processor averages, compares and counts the number of adjacent pixels for assessing weld quality.