Analysis of DR testing blind zone of spherical fuel elements for 10 MW high-temperature gas-cooled reactor

Spherical fuel elements technology is a main innovation of high-temperature gas-cooled reactors (HTGRs), which effectively improves the safety of the reactors for higher stability at high temperature, and their quality is crucial for the safety and reliability of HTDRs. According to a spherical fuel element's structure, the coated fuel particles are not permitted to enter the fuel-free zone and the elements with escaped fuel particles must be removed during the fuel elements' quality control. In this paper, we first introduce a DR imaging system for spherical fuel elements testing applied in Chinese 10 MW high-temperature gas-cooled reactor (HTR-10). Then the blind zone where escaped particles exist is analyzed under the continuous and concrete circular scanning trajectories and the cone-beam imaging geometrical configuration. The dominant scanning parameters determining the size of the blind zone are the rotation step angle and the distance from X-ray source to the tested object. An optimal method of designing the two parameters to decrease the size of the blind zone is proposed so as to satisfy the testing requirements. Finally, the optimal method is verified by computer simulation and some practical identification results are presented.