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Title: Identification of Silver and Palladium in Irradiated TRISO Coated Particles of the AGR-1 Experiment

Evidence of the release of certain metallic fission product through intact tristructural isotropic (TRISO) particles has been seen for decades around the world, as well as in the recent AGR-1 experiment at Idaho National Laboratory (INL). However, understanding the basic mechanism of transport is still lacking. This understanding is important because the TRISO coating is part of the high temperature gas reactor functional containment and critical for the safety strategy for licensing purposes. Our approach to identify fission products in irradiated AGR-1 TRISO fuel using scanning transmission electron microscopy (STEM), Electron Energy Loss Spectroscopy (EELS) and Energy Filtered TEM (EFTEM), has led to first-of-a-kind data at the nano-scale indicating the presence of silver at triple points and grain boundaries of the SiC layer in the TRISO particle. Cadmium was also found in the triple junctions. In this initial study, the silver was only identified in SiC grain boundaries and triple points on the edge of the SiC-IPyC interface up to a depth of approximately 0.5 um. Palladium was identified as the main constituent of micron-sized precipitates present at the SiC grain boundaries. Additionally spherical nano-sized palladium rich precipitates were found inside the SiC grains. These nano-sized Pd precipitates were distributedmore » up to a depth of 5 um away from the SiC-IPyC interlayer. No silver was found in the center of the micron-sized fission product precipitates using these techniques, although silver was found on the outer edge of one of the Pd-U-Si containing precipitates which was facing the IPyC layer. Only Pd-U containing precipitates were identified in the IPyC layer and no silver was identified in the IPyC layer. The identification of silver alongside the grain boundaries and the findings of Pd alongside grain boundaries as well as inside the grains, provide significant knowledge for understanding silver and palladium transport in TIRSO fuel, which has been the topic of international research for the past forty years. Additionally the usefulness of the advanced electron microscopic techniques for TRISO coated particle research is demonstrated in this paper.« less
 [1] ;  [2] ;  [3]
  1. Idaho National Laboratory (INL), Idaho Falls, ID (United States). Fuel Performance and Design Dept.
  2. Idaho National Laboratory (INL), Idaho Falls, ID (United States). Materials Science and Engineering Dept.
  3. Boise State Univ., IA (United States). Dept. of Materials Science and Engineering; Center for Advanced Energy Studies, Idaho Falls, ID (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0022-3115; TRN: US1400357
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Nuclear Materials; Journal Volume: 446; Journal Issue: 1-3
Research Org:
Idaho National Laboratory (INL), Idaho Falls, ID (United States)
Sponsoring Org:
Country of Publication:
United States
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS SiC; silver transport; TRISO coated particle; ; PALLADIUM