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Title: Summary report on UO 2 thermal conductivity model refinement and assessment studies

Abstract

Uranium dioxide (UO 2) is the most commonly used fuel in light water nuclear reactors and thermal conductivity controls the removal of heat produced by fission, therefore, governing fuel temperature during normal and accident conditions. The use of fuel performance codes by the industry to predict operational behavior is widespread. A primary source of uncertainty in these codes is thermal conductivity, and optimized fuel utilization may be possible if existing empirical models were replaced with models that incorporate explicit thermal conductivity degradation mechanisms during fuel burn-up. This approach is able to represent the degradation of thermal conductivity due to each individual defect type, rather than the overall burn-up measure typically used which is not an accurate representation of the chemical or microstructure state of the fuel that actually governs thermal conductivity and other properties. To generate a mechanistic thermal conductivity model, molecular dynamics (MD) simulations of UO 2 thermal conductivity including representative uranium and oxygen defects and fission products are carried out. These calculations employ a standard Buckingham type interatomic potential and a potential that combines the many-body embedded atom method potential with Morse-Buckingham pair potentials. Potential parameters for UO 2+x and ZrO 2 are developed for the latter potential.more » Physical insights from the resonant phonon-spin scattering mechanism due to spins on the magnetic uranium ions have been introduced into the treatment of the MD results, with the corresponding relaxation time derived from existing experimental data. High defect scattering is predicted for Xe atoms compared to that of La and Zr ions. Uranium defects reduce the thermal conductivity more than oxygen defects. For each defect and fission product, scattering parameters are derived for application in both a Callaway model and the corresponding high-temperature model typically used in fuel performance codes. The model is validated by comparison to low-temperature experimental measurements on single crystal hyper-stoichiometric UO 2+x samples and high-temperature literature data. Ongoing works include investigation of the effect of phase separation to UO 2+U 4O 9 on the low temperature thermal conductivity of UO 2+x, and modeling of thermal conductivity using the Green-Kubo method. Ultimately, this work will enable more accurate fuel performance simulations as well as extension to new fuel types and operating conditions, all of which improve the fuel economics of nuclear energy and maintain high fuel reliability and safety.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [2];  [2];  [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Imperial College, London (United Kingdom)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1342869
Report Number(s):
LA-UR-16-28212
DOE Contract Number:  
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS

Citation Formats

Liu, Xiang-Yang, Cooper, Michael William Donald, Mcclellan, Kenneth James, Lashley, Jason Charles, Byler, Darrin David, Bell, B. D.C., Grimes, R. W., Stanek, Christopher Richard, and Andersson, David Ragnar. Summary report on UO2 thermal conductivity model refinement and assessment studies. United States: N. p., 2017. Web. doi:10.2172/1342869.
Liu, Xiang-Yang, Cooper, Michael William Donald, Mcclellan, Kenneth James, Lashley, Jason Charles, Byler, Darrin David, Bell, B. D.C., Grimes, R. W., Stanek, Christopher Richard, & Andersson, David Ragnar. Summary report on UO2 thermal conductivity model refinement and assessment studies. United States. doi:10.2172/1342869.
Liu, Xiang-Yang, Cooper, Michael William Donald, Mcclellan, Kenneth James, Lashley, Jason Charles, Byler, Darrin David, Bell, B. D.C., Grimes, R. W., Stanek, Christopher Richard, and Andersson, David Ragnar. Fri . "Summary report on UO2 thermal conductivity model refinement and assessment studies". United States. doi:10.2172/1342869. https://www.osti.gov/servlets/purl/1342869.
@article{osti_1342869,
title = {Summary report on UO2 thermal conductivity model refinement and assessment studies},
author = {Liu, Xiang-Yang and Cooper, Michael William Donald and Mcclellan, Kenneth James and Lashley, Jason Charles and Byler, Darrin David and Bell, B. D.C. and Grimes, R. W. and Stanek, Christopher Richard and Andersson, David Ragnar},
abstractNote = {Uranium dioxide (UO2) is the most commonly used fuel in light water nuclear reactors and thermal conductivity controls the removal of heat produced by fission, therefore, governing fuel temperature during normal and accident conditions. The use of fuel performance codes by the industry to predict operational behavior is widespread. A primary source of uncertainty in these codes is thermal conductivity, and optimized fuel utilization may be possible if existing empirical models were replaced with models that incorporate explicit thermal conductivity degradation mechanisms during fuel burn-up. This approach is able to represent the degradation of thermal conductivity due to each individual defect type, rather than the overall burn-up measure typically used which is not an accurate representation of the chemical or microstructure state of the fuel that actually governs thermal conductivity and other properties. To generate a mechanistic thermal conductivity model, molecular dynamics (MD) simulations of UO2 thermal conductivity including representative uranium and oxygen defects and fission products are carried out. These calculations employ a standard Buckingham type interatomic potential and a potential that combines the many-body embedded atom method potential with Morse-Buckingham pair potentials. Potential parameters for UO2+x and ZrO2 are developed for the latter potential. Physical insights from the resonant phonon-spin scattering mechanism due to spins on the magnetic uranium ions have been introduced into the treatment of the MD results, with the corresponding relaxation time derived from existing experimental data. High defect scattering is predicted for Xe atoms compared to that of La and Zr ions. Uranium defects reduce the thermal conductivity more than oxygen defects. For each defect and fission product, scattering parameters are derived for application in both a Callaway model and the corresponding high-temperature model typically used in fuel performance codes. The model is validated by comparison to low-temperature experimental measurements on single crystal hyper-stoichiometric UO2+x samples and high-temperature literature data. Ongoing works include investigation of the effect of phase separation to UO2+U4O9 on the low temperature thermal conductivity of UO2+x, and modeling of thermal conductivity using the Green-Kubo method. Ultimately, this work will enable more accurate fuel performance simulations as well as extension to new fuel types and operating conditions, all of which improve the fuel economics of nuclear energy and maintain high fuel reliability and safety.},
doi = {10.2172/1342869},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Feb 03 00:00:00 EST 2017},
month = {Fri Feb 03 00:00:00 EST 2017}
}

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