Qualification of HTR pebbles by X-ray tomography and thermal analysis

Knowledge of the TRISO particle distributions inside HTR fuel pebbles or compacts may help manufacturers to improve the quality of their fuel by providing feedback during the development phase. In a joint program, NRG and JRC-IE develop a fast method to obtain these distributions non-destructively, based on X-ray tomography. The coordinates of the individual TRISO particles are extracted from a tomographic reconstruction of a pebble. The particle distributions are then partially characterized by the distributions of nearest neighbor distances. In addition, the temperature distribution during operation is estimated by assigning power to each particle while using the pebble edge temperature as a boundary condition. The whole procedure was applied to 31 pebbles fabricated in the 1980s in the framework of the German HTR fuel qualification program.