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 124Nuclear Science User Facilities 70 Investigation of the Chemical State of Ag and Pd in SiC Shell of Irradiated TRISO Particles via XAFS Kurt Terrani – Oak Ridge National Laboratory – terranika@ornl.gov Tristructural isotropic (TRISO) fuel particles consist of a fuel kernel contained within a multiple ceramic spherical coating shells. The purpose of these ceramic coating layers, namely graphite and silicon carbide (SiC), is to limit the release of radionuclide fission prod- ucts from the fuel kernel. However, a number of these fission products, particularly precious metals such as Ag, do transport within these layers under reactor normal operating and off-normal conditions. This study examines the mechanism of transport of these species in the SiC coating layer of TRISO particles. Project Description TRISO fuel form has enjoyed decades of development and testing and is currently consid- ered a mature technology. This fuel form, originally developed for high temperature gas-cooled reactor (HTGR) applications, is now being considered for a number of other reactor platforms. To further enhance the safety of these reactors, the mechanism of transport and release of a few select problematic radionuclides, namely Ag and Pd, from these particles needs to be understood. A multitude of compu- tational studies exist that have examined the various possibilities for the transport of these species This experiment for the first time provides insights into specific mechanisms of radionuclide transport in irradiated TRISO particles, providing the basis for fundamental understating that in turn allows informed enhancements to the fuel design. Figure. 1. Palladium XAFS in SiC shells from the various particles compared with metallic Pd foil that clearly shows a different character.