Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 76 Page 77 Page 78 Page 79 Page 80 Page 81 Page 82 Page 83 Page 84 Page 85 Page 86 Page 87 Page 88 Page 89 Page 90 Page 91 Page 92 Page 93 Page 94 Page 95 Page 96 Page 97 Page 98 Page 99 Page 100 Page 101 Page 102 Page 103 Page 104 Page 105 Page 106 Page 107 Page 108 Page 109 Page 110 Page 111 Page 112 Page 113 Page 114 Page 115 Page 116 Page 117 Page 118 Page 119 Page 120 Page 121 Page 122 Page 123 Page 1242015 | ANNUAL REPORT 99 Project Description TheTRISO particle is a promising candidate as fuel for HTGR.TheTRISO coating is part of the HTGR functional containment and critical for the safety strategy for licensing purposes. This study aims at obtaining accurate compositional information and three- dimensional (3-D) spatial distribution of FPs in the SiC layer of neutron irradiatedTRISO fuel by using the APT technique.This information will assist in gaining insight into the transport mechanisms of FP, particularly Ag, Pd, released from neutron irradiatedTRISO fuel. Research that has been performed provided information on elements potentially present in the FP precipi- tates, but no in-depth characterization of composition and distribution of the precipitates has been concluded yet. Knowledge of the accurate composi- tion and spatial distribution of the FPs is critical to understand their formation and transport.This proposed study continues the APT study part of completed RTE proposal with University ofWisconsin in 2014 (Title: STEM/LEAP Study of Fission Product Transportation in Neutron Irradiated TRISO Fuel Particles) and research conducted under the INL Advanced Gas Reactor (AGR) program. If successful, the obtained data will contribute to understanding the FP transport mecha- nisms in SiC and providing feedback to improve design ofTRISO coating to reduce release of FP from theTRISO coated particles. Accomplishments The goals of this research are to identify and quantify fission products (in particular Ag and Pd).The research plan was designed byYaqiaoWu and Isabella J van Rooyen.This research was conducted primarily byYaqiao Wu (TEM, LEAP characterizations and data analyses) and the design, and availability of the APT research samples were primarily performed by Isabella J van Rooyen. HaimingWen participated in an EML scheduling meeting by representing Idaho National Laboratory as the co‑PI at this meeting. CAES MaCS staff, including JoannaTaylor and Kristi Moser‑Mcintire, were of great help with handlingTRISO fuels and sched- uling equipment times.Two sample series of unirradiated surrogateTRISO fuel (supplied by John Hunn from Oak Ridge National Laboratory) and irradi- atedTRISO fuel from Compact 6-3-2 (from the AGR‑1 experiment by INL) were characterized.APT tips of unirra- diated surrogate samples were prepared at MaCS, Center for Advanced Energy Studies (CAES) by Jatuporn Burns using a FEI Quanta Focused Ion Beam (FIB).The irradiated samples were prepared at the MFC-EML by James Madden using a FEI Quanta FIB.TEM/ EDS (FEI Tecnai G2 F30 FEG STEM) characterization on the tips before APT experiments (CAMECA LEAP 4000X HR) were conducted at MaCS, CAES.The APT data were analyzed by using CAMECA IVAS software package. This is an unique result because for the first time we see Ag, Pd,and U together in a three- dimensional atomic structure. This is also the first time that APT was successfully applied to neutron irradiated SiC work to identify fission products. — Dr.Isabella J.van Rooyen TRISO Fuel Advanced Microscopy and Micro-Analysis Lead