Ceramography of irradiated TRISO fuel from the AGR-2 experiment

Ceramography was performed on cross sections from four tristructural isotropic (TRISO) coated particle fuel compacts selected from the AGR-2 experiment, which was irradiated between June 2010 and October 2013 in the Advanced Test Reactor (ATR). The individual fuel specimens examined in this study contained coated particles with either uranium oxide (UO2) kernels or uranium oxide/uranium carbide (UCO) kernels that were irradiated to final burnup values between 9.0 and 11.5% FIMA. These examinations were intended to explore kernel and coating morphology evolution during irradiation. This included observations of kernel porosity, kernel swelling, and irradiation-induced TRISO coating layer fracture and separation. Variations in behavior within a specific cross section, which could be related to temperature or burnup gradients within the fuel compact, were also explored. Results were compared with similar investigations performed as part of the earlier AGR-1 irradiation experiment. The criteria for categorizing AGR-1 particle post-irradiation morphologies during ceramographic exams were applied to the AGR-2 compact particles examined. This paper presents the results of the AGR-2 examinations and discusses the key implications for fuel irradiation performance.