Associations of Pd, U and Ag in the SiC layer of neutron-irradiated TRISO fuel

•Fission products in the SiC layer of a neutron-irradiated TRISO particle were analyzed.•Pd, Ag and U found in grain boundary, matrix and triple junction precipitates.•U never found alone or with Ag, only associated with Pd.•Not all boundaries and triple junctions had fission products.•Grain boundary crystallographic parameters likely a factor in migration behavior. Knowledge of the associations and composition of fission products in the neutron irradiated SiC layer of high-temperature gas reactor TRISO fuel is important to the understanding of various aspects of fuel performance that presently are not well understood. Recently, advanced characterization techniques have been used to examine fuel particles from the Idaho National Laboratory’s AGR-1 experiment. Nano-sized Ag and Pd precipitates were previously identified in grain boundaries and triple points in the SiC layer of irradiated TRISO nuclear fuel. Continuation of this initial research is reported in this paper and consists of the characterization of a relatively large number of nano-sized precipitates in three areas of the SiC layer of a single irradiated TRISO nuclear fuel particle using standardless EDS analysis on focused ion beam-prepared transmission electron microscopy samples. Composition and distribution analyses of these precipitates, which were located on grain boundaries, triple junctions and intragranular precipitates, revealed low levels, generally