Molecular dynamics simulation of local structure and vibrational spectrum of uranyl (UO{sub 2}){sup 2+} in vitreous B{sub 2}O{sub 3}.

Conference · Fri Nov 03 00:00:00 EST 2000

OSTI ID:768603

Zhuang, Z -H; Liu, G K; Beitz, J V

Laser spectroscopic and extended X-ray absorption fine structure (EXAFS) spectra have shown that uranium in B{sub 2}O{sub 3} glass matrix forms uranyl in the electronic configuration of (UO{sub 2}){sup 2+},but its surrounding structure is not well known. Understanding of uranyl local structure, ion-ligand interaction, and chemical stability on the nanometer scale in glasses is essential in management of long-term performance of high-level nuclear wastes after disposal in a geologic repository. In the present work, the structure, phonon density of states, and vibrational spectrum of vitreous B{sub 2}O{sub 3} and the surrounding environment that contains a uranyl ion have been studied using a molecular dynamics (MD) simulation method that utilizes the Born-Mayer-Huggins and Coulomb pair potentials and the Stillinger-Weber three-body potential. A system of 406 ions was considered in our calculation. Simulation of a thermal quenching from 3000 K to 300 K was performed to generate a uniform and equilibrium model glass matrix before structure configuration and vibrational frequencies were obtained from the system. The structure of the simulated glass is in agreement with that reported by Krogh-Moe and Mozzi et al. The characteristic network of planar boroxol (B{sub 3}O{sub 6}) rings is evident in the simulated system. A configuration of a U{sup 6+} cation in the vitreous B{sub 2}O{sub 3} matrix is shown in Fig. 1. It is shown that a nearly linear (UO{sub 2}){sup 2+} uranyl ion is coordinated by four equatorial oxygen anions in an approximately planar arrangement. The U-O bond length is approximately 0.178 nm for the axial oxygen and 0.254 nm for the equatorial oxygen, which is in good agreement with the U-O distances obtained from fitting EXAFS spectra. Based on the simulated model structure, the uranyl vibrational spectrum is simulated and compared with experimental results obtained using site-selective fluorescence line narrowing (FLN) techniques.

• Research Organization: Argonne National Lab., IL (US)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: W-31-109-ENG-38
• OSTI ID: 768603
• Report Number(s): ANL/CHM/CP-103227; TRN: US0102903
• Resource Relation: Conference: 2001 International Conference on Computational Nanoscience, Hilton Head Island, SC (US), 03/19/2001--03/21/2000; Other Information: PBD: 3 Nov 2000
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
BOND LENGTHS
FINE STRUCTURE
LASER SPECTROSCOPY
LINE NARROWING
HIGH-LEVEL RADIOACTIVE WASTES
URANYL COMPOUNDS
X-RAY SPECTROSCOPY
GLASS
BORON OXIDES
MOLECULAR DYNAMICS METHOD