Co-operativity among defect sites in AnO2+ and An4O9 (An = U, Np or Pu)

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Physical Review. B, Condensed Matter and Materials Physics

OSTI ID:960582

Andersson, Anders David ^[1]; Lezama Pacheco, Juan ^[1]; Uberuaga, Blas P ^[1]; Conradson, Steven D ^[1]

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1. Los Alamos National Laboratory

Actinide dioxides derived from the AnO{sub 2} fluorite lattice are of high technological relevance due to their application in nuclear reactor fuels. Oxidation of AnO{sub 2} compounds emerges as a central theme in fuel fabrication, reactor operation, long-term storage forms for both spent fuels and surplus weapons materials, and environmental actinide migration. In this paper, we use density functional theory calculations to study the oxidation of uranium, neptunium and plutonium dioxides, AnO{sub 2} (An = U, Np or Pu), in O{sub 2} and O{sub 2}/H{sub 2}O environments. We pay particular attention to the formation of oxygen clusters (co-operativity) in AnO{sub 2+x} and how this phenomenon govern oxidation thermodynamics and the development of ordered An{sub 4}O{sub 9} compounds. The so-called split di-interstitial, which is composed of two nearest neighbor octahedral oxygen interstitials that are distorted in such a way that they dislocate one regular fluorite lattice oxygen ion to form a cluster of triangular geometry, is predicted to be the fundamental building block of the most stable cluster configurations. We also identify how the formation of oxygen defect clusters and the degree of oxidation in AnO{sub 2+x} are both governed by the characer of the An-5f to excess O-2p charger transfer, i.e. the charge transfer to the O-2p orbitals of the interstitial-like (+x) ions, and the ability of the excess O-2p orbitals to hybridize with regular fluorite lattice ions.

• Research Organization: Los Alamos National Laboratory (LANL)
• Sponsoring Organization: DOE
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 960582
• Report Number(s): LA-UR-08-05368; LA-UR-08-5368
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACTINIDES
BUILDINGS
CHARGES
DEFECTS
DENSITY
DENSITY FUNCTIONAL METHOD
ENVIRONMENTAL TRANSPORT
FABRICATION
FLUORITE
INTERSTITIALS
IONS
MATERIALS
MIGRATION
NEPTUNIUM
NUCLEAR FUELS
OXIDATION
OXYGEN
OXYGEN IONS
PLUTONIUM DIOXIDE
REACTOR OPERATION
REACTORS
SPENT FUELS
STORAGE
THERMODYNAMICS
URANIUM
WEAPONS