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

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,more » 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.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1]
  1. Los Alamos National Laboratory
Publication Date:
OSTI Identifier:
960582
Report Number(s):
LA-UR-08-05368; LA-UR-08-5368
Journal ID: ISSN 1098-0121; TRN: US1002078
DOE Contract Number:
AC52-06NA25396
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B
Research Org:
Los Alamos National Laboratory (LANL)
Sponsoring Org:
DOE
Country of Publication:
United States
Language:
English
Subject:
36; ACTINIDES; BUILDINGS; CHARGES; DEFECTS; DENSITY; DENSITY FUNCTIONAL METHOD; ENVIRONMENTAL TRANSPORT; FABRICATION; FLUORITE; NUCLEAR FUELS; INTERSTITIALS; IONS; MATERIALS; MIGRATION; NEPTUNIUM; OXIDATION; OXYGEN; OXYGEN IONS; PLUTONIUM DIOXIDE; REACTOR OPERATION; REACTORS; SPENT FUELS; STORAGE; THERMODYNAMICS; URANIUM; WEAPONS