Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “U3Si”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on U3Si by Materials Project

U3Si is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. U is bonded to eight equivalent U and four equivalent Si atoms to form distorted UU8Si4 cuboctahedra that share corners with twelve equivalent UU8Si4 cuboctahedra, edges with eight equivalent SiU12 cuboctahedra, edges with sixteen equivalent UU8Si4 cuboctahedra, faces with four equivalent SiU12 cuboctahedra, and faces with fourteen equivalent UU8Si4 cuboctahedra. All U–U bond lengths are 3.01 Å. All U–Si bond lengths are 3.01 Å. Si is bonded to twelve equivalent U atoms to form SiU12 cuboctahedra that share corners with twelve equivalent SiU12 cuboctahedra, edges with twenty-four equivalent UU8Si4 cuboctahedra, faces with six equivalent SiU12 cuboctahedra, and faces with twelve equivalent UU8Si4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U3Si by Materials Project

U3Si is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. there are two inequivalent U sites. In the first U site, U is bonded to eight equivalent U and four equivalent Si atoms to form distorted UU8Si4 cuboctahedra that share corners with twelve equivalent UU8Si4 cuboctahedra, edges with eight equivalent SiU12 cuboctahedra, faces with four equivalent SiU12 cuboctahedra, and faces with six equivalent UU8Si4 cuboctahedra. There are four shorter (2.86 Å) and four longer (3.15 Å) U–U bond lengths. All U–Si bond lengths are 3.01 Å. In the second U site, U is bonded in a 12-coordinate geometry to eight U and four equivalent Si atoms. All U–U bond lengths are 3.02 Å. All U–Si bond lengths are 3.01 Å. Si is bonded to twelve U atoms to form SiU12 cuboctahedra that share corners with twelve equivalent SiU12 cuboctahedra, edges with eight equivalent UU8Si4 cuboctahedra, faces with four equivalent UU8Si4 cuboctahedra, and faces with six equivalent SiU12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U3Si by Materials Project

U3Si is beta Cu3Ti-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are six inequivalent U sites. In the first U site, U is bonded in a 4-coordinate geometry to eight U and four Si atoms. There are a spread of U–U bond distances ranging from 2.90–3.14 Å. All U–Si bond lengths are 3.01 Å. In the second U site, U is bonded in a 4-coordinate geometry to eight U and four Si atoms. There are a spread of U–U bond distances ranging from 2.90–3.14 Å. All U–Si bond lengths are 3.01 Å. In the third U site, U is bonded in a 12-coordinate geometry to eight U and four Si atoms. There are two shorter (2.81 Å) and two longer (3.19 Å) U–U bond lengths. All U–Si bond lengths are 3.01 Å. In the fourth U site, U is bonded in a 12-coordinate geometry to eight U and four Si atoms. There are a spread of U–U bond distances ranging from 2.81–3.18 Å. All U–Si bond lengths are 3.01 Å. In the fifth U site, U is bonded in a 12-coordinate geometry to eight U and four Si atoms. There are three shorter (3.01 Å) and one longer (3.02 Å) U–Si bond lengths. In the sixth U site, U is bonded in a 12-coordinate geometry to eight U and four Si atoms. There are two shorter (3.01 Å) and two longer (3.02 Å) U–Si bond lengths. There are two inequivalent Si sites. In the first Si site, Si is bonded to twelve U atoms to form a mixture of corner and face-sharing SiU12 cuboctahedra. In the second Si site, Si is bonded to twelve U atoms to form a mixture of corner and face-sharing SiU12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Evaluation of Thermal Neutron Scattering Cross Section of Uranium Silicide with Ab Initio Lattice Dynamics

Uranium silicide (U 3 Si 2 ) is a candidate material for the high-density nuclear fuel in commercial light water reactors [1], [2]. Its higher uranium density, 11.3 g-U/cm3, compared to that of uranium dioxide (UO 2 ), 9.7 g-U/cm3, can improve the performance of a nuclear reactor while using low enriched uranium (LEU) and diversify the choice of cladding materials [1]–[3]. It also has a higher thermal conductivity than UO 2 , which can reduce the thermal stress on the material caused by a temperature gradient across the fuel pellet and provide a larger margin for some postulated accidents [1], [2], [4]. Furthermore, compared to U3Si, another high-density fuel candidate, it has better resistance to in-pile swelling due to less irradiation-induced rapid amorphization [1], [3]. Corresponding to its importance in nuclear engineering, many previous studies have reported the properties of U3Si2. Experiments showed that U 3 Si 2 is a paramagnetic (PM) metal, where a slight linear increase in magnetic susceptibility was measured with increasing temperature [5], [6]. In addition, thermodynamic quantities such as thermal expansion coefficient, heat capacity, and thermal conductivity were experimentally determined over a wide temperature range [1], [7], [8]. In several computational studies, ab initio atomistic simulations based on density functional theory (DFT) were performed to calculate various properties including elastic constants, electronic density of states (DOS), and phonon dispersion curves [9]–[12]. Nevertheless, thermal neutron scattering cross sections, which are critical to the prediction of the parameters in reactor physics that are ultimately related to reactor criticality, have not yet been evaluated for U3Si2. The scattering cross section can be calculated from the phonon DOS, or the energy spectrum of lattice vibrations, of the crystalline system [13], [14]. However, there is also no experimental data available for the phonon DOS of U 3 Si 2 . While some computational studies reported the phonon DOS and/or dispersion curves from ab initio simulations [9]–[12], the accuracy cannot be guaranteed because it is unclear whether the spin-polarization behavior of PM U 3 Si 2 was properly described. In the present study, the thermal neutron scattering cross section for U 3 Si 2 is evaluated for the first time by calculating the phonon DOS for U3Si2 from ab initio lattice dynamics (AILD) simulations based on DFT. First, U 3 Si 2 is modeled based on the experimental structure, and AILD simulations are performed on the modeled U3Si2 to optimize the structure. Next, AILD simulations are performed for supercells with atomic displacement to calculate Hellmann-Feynman forces. Based on the calculated forces, partial phonon DOSs for U and Si are obtained, and the thermal neutron scattering law (TSL) for U 3 Si 2 is finally evaluated. To verify the accuracy of the calculations in the present study, the calculation results are compared with experimental data on the structure and heat capacity of U3Si2 [1], [7], [8], [15].

Geometry Optimization↗