Micro/Nano-Structural Examination and Fission Product Identification in Neutron Irradiated Agr-1 TRISO Fuel
Advanced electron microscopic and micro-analysis techniques were developed and applied to study irradiation effects and fission-product behavior in selected low-enriched uranium-oxide/uranium-carbide tristructural-isotropic (TRISO)-coated particles from fuel compacts in four capsules irradiated to burnups of 11.2 to 19.6% fissions per initial metal atom (FIMA) consisting of Baseline, Variant 1, and Variant 3 fuel types. Trend analysis shows precipitates were mostly random in their distribution along the perimeter of the inner pyrolytic carbon-silicon carbide (IPyC-SiC) interlayer with only weak association with kernel protrusion and buffer fractures. Pd is dominantly found in most precipitates in both intra and intergranular locations. Nano-sized Ag is predominantly found in grain boundaries and triple points with only two findings of Ag inside a SiC grain in two different compacts (Baseline and Variant 3 fueled compacts). Generally, more element combinations exist for precipitates from particles with relatively low Ag retention compared to particles with relatively high Agretention irrespective of fuel type. This study shows the presence of Cs in particles from all compacts evaluated. From this work, no single fission product mechanism hypothesis can be reported. The complexity of mechanisms is further highlighted by the multiple variations of elemental combinations found in the more than 700 fission product precipitates examined. It seems that movement of Ag is not assisted by a specific element in all cases. Therefore, it is not necessarily true that a chemical-assisted transport mechanism is dominant. The presence of Ag predominantly on grain boundaries suggests that a grain boundary transport mechanism may be prominent. Studies to determine the effect of neutron damage are recommended for future work.
I. J. Van Rooyen et al., "Micro/Nano-Structural Examination and Fission Product Identification in Neutron Irradiated Agr-1 TRISO Fuel," International Topical Meeting on High Temperature Reactor Technology, HTR 2016, pp. 652 - 669, American Nuclear Society (ANS), Nov 2016.
8th International Topical Meeting on High Temperature Reactor Technology (2016: Nov. 6-10, Las Vegas, NV)
Materials Science and Engineering
International Standard Book Number (ISBN)
Article - Conference proceedings
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01 Nov 2016