A 3D-reconstruction research on the visual liquid-pebble bed

Abstract Background: Thorium-based molten salt reactor with solid fuel (TMSR-SF) is one type of the fourth nuclear power plant which combines high-temperature graphite-matrix coated-particle pebble fuel for high temperature gas-cooled reactors and liquid salts developed for the molten salt reactors. The design of TMSR-SF requires detailed understanding of the packing structure of the pebble bed in reactor core. Purpose: This article is aimed to explore the effectiveness of refractive index matched scanning technique (RIMS) in the 3D-reconstruction of reactor core. Methods: The cross sections of the pebble bed are imaged by a charge-coupled device (CCD), then the threshold transformation, filter transformation and Hough transformation are used to process the images, and the coordinates of points on the spheres'edge are extracted. Then an algorithm is used to acquire the relative center coordinates of each sphere. Results: The result shows that excluding irrelevant distractors can improve the accuracy of the 3D-reconstruction, and creating region of interest (ROI) to make threshold transformation is a good method to enhance circles'edges, and when the circles in the images distort, minimum bounding rectangle (MBR) functions is more effective than Hough circle transformation. Conclusion: Our scheme of reconstruction can reconstruct the 3D packing structure of the pebble bed with the mean distance-overlapped which is 1.43 mm, and this precision needs to be improved later. (authors)