Synchrotron phase-contrast CT to segment the structure boundaries of a TRISO-coated particle

Tri-structural Isotropic (TRISO)-coated particle is the fission energy source and the first safety barrier in high temperature gas-cooled reactors (HTGRs). The integrity of TRISO particle should be carefully tested before operation because the shape may affect the failure possibility of the particles, leading to increased risk of fission product release. Due to the large difference in density between the kernel and the coating layers in TRISO particles, traditional X-ray radiography cannot achieve a good image quality in terms of identifying coating layers reliably, while phase-contrast CT has the advantage of being sensitive to boundaries. This paper presents a non-destructive test and evaluation (NDT&E) method to facilitate 3-dimensional (3D) measurement of a TRISO particles structure, using a synchrotron phase-contrast CT. After reconstructed, the TRISO particle was rendered in a 3D space and the thickness and asphericity of the TRISO particles layers were measured. It was found that the thickness of coating layers of the tested particle obeys Gaussian distribution. The deviation of thicknesses of the kernel and the other four layers is - 2.42%, -16.32%, 26.51%, 0.98% and 7.49% compared with the design parameters. The deviation of asphericity of the kernel, IPyC and OPyC layers is - 11.51%, - 0.41% and 3.39%, respectively. The effect of the deviations on the temperature distribution and failure probability calculation of the particle will be investigated in the future.