Nondestructive Measurement of the Coating Thickness in the Simulated TRISO-Coated Fuel Particle for the HTGR

TRISO(tri-isotropic)-coated fuel particle technology is utilized owing to its higher stability at a high temperature and its efficient retention capability for fission products in the HTGR(high temperature gas cooled reactor). The typical spherical TRISO fuel particle with a diameter of about 1 mm is composed of a nuclear fuel kernel and outer coating layers. The coating layers consist of a buffer PyC(pyrolytic carbon) layer, inner PyC(I-PyC) layer, SiC layer, and outer PyC(OPyC) layer. The thickness of the coating layer can be nondestructively measured by the X-ray radiography without generating the radioactive wastes. In this study, digital image processing technology as well as micro X-ray radiography technology was developed to measure the coating thickness for a simulated TRISO-coated fuel particle with a ZrO₂ kernel instead of a UO₂ kernel. At first, the coating thickness was measured by manually observing the coating layer on the radiographic image. Then, the coating thickness was measured by automatically recognizing the coating layer on the radiographic image. The coating thickness could be measured more effectively by the automatic recognition method. (author)