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Title: Near Surface Stoichiometry in UO 2 : A Density Functional Theory Study

Abstract

The mechanisms of oxygen stoichiometry variation in UO 2at different temperature and oxygen partial pressure are important for understanding the dynamics of microstructure in these crystals. However, very limited experimental studies have been performed to understand the atomic structure of UO 2near surface and defect effects of near surface on stoichiometry in which the system can exchange atoms with the external reservoir. In this study, the near (110) surface relaxation and stoichiometry in UO 2have been studied with density functional theory (DFT) calculations. On the basis of the point-defect model (PDM), a general expression for the near surface stoichiometric variation is derived by using DFT total-energy calculations and atomistic thermodynamics, in an attempt to pin down the mechanisms of oxygen exchange between the gas environment and defected UO 2. By using the derived expression, it is observed that, under poor oxygen conditions, the stoichiometry of near surface is switched from hyperstoichiometric at 300 K with a depth around 3 nm to near-stoichiometric at 1000 K and hypostoichiometric at 2000 K. Furthermore, at very poor oxygen concentrations and high temperatures, our results also suggest that the bulk of the UO 2prefers to be hypostoichiometric, although the surface is near-stoichiometric.

Authors:
 [1];  [2];  [2];  [2];  [1]
  1. Idaho National Laboratory, Idaho Falls, ID 83415, USA
  2. University of Florida, Gainesville, FL 32611, USA
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Materials Science of Nuclear Fuel (CMSNF)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1369983
DOE Contract Number:
AC07-05ID14517
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemistry; Journal Volume: 2015; Related Information: CMSNF partners with Idaho National Laboratory (lead); Colorado School of Mines; University of Florida; Oak Ridge National Laboratory; Purdue University; University of Wisconsin at Madison
Country of Publication:
United States
Language:
English

Citation Formats

Yu, Jianguo, Valderrama, Billy, Henderson, Hunter B., Manuel, Michele V., and Allen, Todd. Near Surface Stoichiometry in UO2 : A Density Functional Theory Study. United States: N. p., 2015. Web. doi:10.1155/2015/142510.
Yu, Jianguo, Valderrama, Billy, Henderson, Hunter B., Manuel, Michele V., & Allen, Todd. Near Surface Stoichiometry in UO2 : A Density Functional Theory Study. United States. doi:10.1155/2015/142510.
Yu, Jianguo, Valderrama, Billy, Henderson, Hunter B., Manuel, Michele V., and Allen, Todd. Thu . "Near Surface Stoichiometry in UO2 : A Density Functional Theory Study". United States. doi:10.1155/2015/142510.
@article{osti_1369983,
title = {Near Surface Stoichiometry in UO2 : A Density Functional Theory Study},
author = {Yu, Jianguo and Valderrama, Billy and Henderson, Hunter B. and Manuel, Michele V. and Allen, Todd},
abstractNote = {The mechanisms of oxygen stoichiometry variation in UO2at different temperature and oxygen partial pressure are important for understanding the dynamics of microstructure in these crystals. However, very limited experimental studies have been performed to understand the atomic structure of UO2near surface and defect effects of near surface on stoichiometry in which the system can exchange atoms with the external reservoir. In this study, the near (110) surface relaxation and stoichiometry in UO2have been studied with density functional theory (DFT) calculations. On the basis of the point-defect model (PDM), a general expression for the near surface stoichiometric variation is derived by using DFT total-energy calculations and atomistic thermodynamics, in an attempt to pin down the mechanisms of oxygen exchange between the gas environment and defected UO2. By using the derived expression, it is observed that, under poor oxygen conditions, the stoichiometry of near surface is switched from hyperstoichiometric at 300 K with a depth around 3 nm to near-stoichiometric at 1000 K and hypostoichiometric at 2000 K. Furthermore, at very poor oxygen concentrations and high temperatures, our results also suggest that the bulk of the UO2prefers to be hypostoichiometric, although the surface is near-stoichiometric.},
doi = {10.1155/2015/142510},
journal = {Journal of Chemistry},
number = ,
volume = 2015,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 2015},
month = {Thu Jan 01 00:00:00 EST 2015}
}