X-ray computed tomography of deconsolidated TRISO Particles from the AGR-5/6/7 irradiation experiment capsule 1 Compact

Abstract

X-ray Computed Tomography (XCT) was performed on TRISO particles from fuel Compact 1-7-9 from Capsule 1 of the AGR-5/6/7 irradiation experiment. Compact 1–7–9 was in the vicinity of overheated thermocouples that released transition metals and caused significant damage and failure of TRISO particles within regions of Capsule 1. Four particles, Particles A–D, were non-destructively examined in three-dimensions (3D). Particle B was found to have degraded silicon carbide (SiC) and significant amounts of Ni, actinides, and fission products that contributed to this degradation. The nickel (Ni) showed some evidence of penetration into Particle B from the exterior surface of the silicon carbide layer. The kernels of Particles A, C, and D were analyzed for their size, shape, and observed porosity. A density gradient was observed in the kernels, which may be nascent kernel migration observed in fuel with higher irradiation temperatures. In addition to the kernels, Particles A, C, and D possessed large clusters of dense material that were grouped primarily to one side of the particle located at the buffer/inner pyrolytic carbon interface. These clusters were attributed to nickel migration into the particle interiors, which was confirmed with scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDS).