Results for “Pd-U” | Engineering Papers

DOE OSTI2020

Electron Microscopic Examination of an Irradiated TRISO Coated Particle of AGR-2 Experiment: AGR2-222-RS019

The transmission electron microscopic (TEM) examination of an irradiated tristructural isotropic (TRISO) coated particle from advanced gas reactor (AGR) 2 fuel Compact 2-2-2 is presented in this report. Compact 2-2-2 refers to the compact in Capsule 2 at Level 2 of Stack 2. The examination on AGR2 222 RS019 is focused on the interface between the silicon carbide (SiC) to inner pyrolytic carbon (IPyC) layer, central part of SiC, and the interface between SiC and outer pyrolytic carbon layer. The SiC grain boundary distribution and associated fission product precipitates were characterized by scanning transmission electron microscopy (STEM) energy dispersive spectroscopy (EDS), and precession electron diffraction (PED) in the transmission electron microscope. Two separate locations on SiC layer were selected for on the basis of the intact of the buffer layer in the irradiated TRISO particle. The key observation in this particle is that the compositional nature of grain boundary precipitates is more complex near IPyC/SiC layer where Pd, Pd-Ag, Pd-U containing precipitates can be observed. However, the compositions of precipitate towards outer most region of SiC mainly contain Pd. Ag has been observed in the IPyC/SiC layer in one of the two locations. Comparison of the results to previously irradiated and analyzed, Variant 3, safety tested AGR-1 TRISO particles (AGR1-433-001 and AGR1 222-RS004) showed the grain boundary distributions have some noticeable differences. The differences in coincident site lattice grain boundary and misorientation angles are possibly inherent to the fabrication process. Neutron irradiation induced void distribution has been found to be nonuniform. A high concentration of smaller voids is found at stacking faults compared to those in the SiC matrix. Larger void sizes are observed in the SiC location that is near to the broken buffer layer. This void size variation with integrity of buffer layer can potentially affect the fission product retention. However, the average void size continuously decreases along the radius of SiC in both locations.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2020

Materials Data on UPd3 by Materials Project

UPd3 is Uranium Silicide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent U sites. In the first U site, U is bonded to twelve Pd atoms to form UPd12 cuboctahedra that share corners with six equivalent UPd12 cuboctahedra, edges with twelve equivalent PdU4Pd8 cuboctahedra, faces with six equivalent PdU4Pd8 cuboctahedra, and faces with eight UPd12 cuboctahedra. There are six shorter (2.92 Å) and six longer (2.98 Å) U–Pd bond lengths. In the second U site, U is bonded to twelve Pd atoms to form UPd12 cuboctahedra that share corners with twelve equivalent UPd12 cuboctahedra, edges with twelve equivalent PdU4Pd8 cuboctahedra, faces with six equivalent UPd12 cuboctahedra, and faces with six equivalent PdU4Pd8 cuboctahedra. There are six shorter (2.92 Å) and six longer (2.96 Å) U–Pd bond lengths. There are two inequivalent Pd sites. In the first Pd site, Pd is bonded to four U and eight Pd atoms to form distorted PdU4Pd8 cuboctahedra that share corners with twelve equivalent PdU4Pd8 cuboctahedra, edges with eight UPd12 cuboctahedra, edges with eight equivalent PdU4Pd8 cuboctahedra, faces with four UPd12 cuboctahedra, and faces with four equivalent PdU4Pd8 cuboctahedra. There are a spread of Pd–Pd bond distances ranging from 2.86–2.98 Å. In the second Pd site, Pd is bonded in a distorted square co-planar geometry to four U and four equivalent Pd atoms.

36 MATERIALS SCIENCE↗