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Title: Quantitative MD simulations to assess UO2 thermal conductivity as a function of burnup

Authors:
 [1];  [1];  [1]
  1. Los Alamos National Laboratory
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
DOE/LANL
OSTI Identifier:
1148956
Report Number(s):
LA-UR-14-26153
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
Materials Science(36)

Citation Formats

Liu, Xiang-Yang, Andersson, Anders David Ragnar, and Stanek, Christopher Richard. Quantitative MD simulations to assess UO2 thermal conductivity as a function of burnup. United States: N. p., 2014. Web. doi:10.2172/1148956.
Liu, Xiang-Yang, Andersson, Anders David Ragnar, & Stanek, Christopher Richard. Quantitative MD simulations to assess UO2 thermal conductivity as a function of burnup. United States. doi:10.2172/1148956.
Liu, Xiang-Yang, Andersson, Anders David Ragnar, and Stanek, Christopher Richard. Mon . "Quantitative MD simulations to assess UO2 thermal conductivity as a function of burnup". United States. doi:10.2172/1148956. https://www.osti.gov/servlets/purl/1148956.
@article{osti_1148956,
title = {Quantitative MD simulations to assess UO2 thermal conductivity as a function of burnup},
author = {Liu, Xiang-Yang and Andersson, Anders David Ragnar and Stanek, Christopher Richard},
abstractNote = {},
doi = {10.2172/1148956},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Aug 04 00:00:00 EDT 2014},
month = {Mon Aug 04 00:00:00 EDT 2014}
}

Technical Report:

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  • The thermal conductivity of uranium dioxide (UO 2) fuel is an important materials property that affects fuel performance since it is a key parameter determining the temperature distribution in the fuel, thus governing, e.g., dimensional changes due to thermal expansion, fission gas release rates, etc. [1] The thermal conductivity of UO 2 nuclear fuel is also affected by fission gas, fission products, defects, and microstructural features such as grain boundaries. Here, molecular dynamics (MD) simulations are carried out to determine quantitatively, the effect of irradiation induced point defects on the thermal conductivity of UO 2, as a function of defectmore » concentrations, for a range of temperatures, 300 – 1500 K. The results will be used to develop enhanced continuum thermal conductivity models for MARMOT and BISON by INL. These models express the thermal conductivity as a function of microstructure state-variables, thus enabling thermal conductivity models with closer connection to the physical state of the fuel [2].« less
  • The thermal diffusivity was measured using the laser flash method on sintered uranium dioxide (O/U=2.003, density=10.48X10 kg/m, from 300 to 2773 K), and urania and gadolinia mixed fuel (2,4 and 6 Wt% Gd2O3 content, from 600 to 1850 K). An equation was suggested for near-stoichiometric uranium dioxide over the temperature range 500-3100 K: K=(1-aP)(1/(A+BT)+DTxexp(-E/kT)x(1+H(E/kT+2)(sup 2))), where K in W/(m)(K), P is the fraction of porosity, a=2.74-5.8X10(sup 4-)T, A=3.68X10(sup 2-)(m)(K)/W, B=2.25X10(sup 4-)m/W, D=5.31X10(sup 3-)W/mXK2, H=0.264, E=1.15 ev, k is the Boltzmann constant. The thermal conductivity of UO2-Gd2O3 samples as a function of temperature and Gd2O3 content, X, could be expressed bymore » phonon conduction; K=1/(A+BT) in the temperature range from 600 to 1700 K, where A=2.50 X+0.044(m)(K)/W.« less
  • Thermal conductivity is one of the most important metrics of nuclear fuel performance. Therefore, it is crucial to understand the impact of microstructure features on thermal conductivity, especially since the microstructure evolves with burn-up or time in the reactor. For example, UO{sub 2} fuels are polycrystalline and for high-burnup fuels the outer parts of the pellet experience grain sub-division leading to a very fine grain structure. This is known to impact important physical properties such as thermal conductivity as fission gas release. In a previous study, we calculated the effect of different types of {Sigma}5 grain boundaries on UO{sub 2}more » thermal conductivity and predicted the corresponding Kapitza resistances, i.e. the resistance of the grain boundary in relation to the bulk thermal resistance. There have been reports of pseudoanisotropic effects for the thermal conductivity in cubic polycrystalline materials, as obtained from molecular dynamics simulations, which means that the conductivity appears to be a function of the crystallographic direction of the temperature gradient. However, materials with cubic symmetry should have isotropic thermal conductivity. For this reason it is necessary to determine the cause of this apparent anisotropy and in this report we investigate this effect in context of our earlier simulations of UO{sub 2} Kapitza resistances. Another source of thermal resistance comes from fission products and fission gases. Xe is the main fission gas and when generated in sufficient quantity it dissolves from the lattice and forms gas bubbles inside the crystalline structure. We have performed studies of how Xe atoms dissolved in the UO{sub 2} matrix or precipitated as bubbles impact thermal conductivity, both in bulk UO{sub 2} and in the presence of grain boundaries.« less