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Title: Thermal expansion of UO2+x nuclear fuel rods from a model coupling heat transfer and oxygen diffusion

Abstract

We study the thermal expansion of UO{sub 2+x} nuclear fuel rod in the context of a model coupling heat transfer and oxygen diffusion discussed previously by J.C. Ramirez, M. Stan and P. Cristea [J. Nucl. Mat. 359 (2006) 174]. We report results of simulations performed for steady-state and time-dependent regimes in one-dimensional configurations. A variety of initial- and boundary-value scenarios are considered. We use material properties obtained from previously published correlations or from analysis of previously published data. All simulations were performed using the commercial code COMSOL Multiphysics{sup TM} and are readily extendable to include multidimensional effects.

Authors:
 [1];  [1];  [1];  [2]
  1. Los Alamos National Laboratory
  2. EXPONENT, INC.
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
960472
Report Number(s):
LA-UR-08-04952; LA-UR-08-4952
Journal ID: ISSN 0022-3115; JNUMAM; TRN: US1002048
DOE Contract Number:
AC52-06NA25396
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Nuel.Mat
Country of Publication:
United States
Language:
English
Subject:
11; COUPLING; DIFFUSION; HEAT TRANSFER; NUCLEAR FUELS; OXYGEN; FUEL RODS; THERMAL EXPANSION; URANIUM DIOXIDE

Citation Formats

Mihaila, Bogden, Zubelewicz, Aleksander, Stan, Marius, and Ramirez, Juan. Thermal expansion of UO2+x nuclear fuel rods from a model coupling heat transfer and oxygen diffusion. United States: N. p., 2008. Web.
Mihaila, Bogden, Zubelewicz, Aleksander, Stan, Marius, & Ramirez, Juan. Thermal expansion of UO2+x nuclear fuel rods from a model coupling heat transfer and oxygen diffusion. United States.
Mihaila, Bogden, Zubelewicz, Aleksander, Stan, Marius, and Ramirez, Juan. Tue . "Thermal expansion of UO2+x nuclear fuel rods from a model coupling heat transfer and oxygen diffusion". United States. doi:. https://www.osti.gov/servlets/purl/960472.
@article{osti_960472,
title = {Thermal expansion of UO2+x nuclear fuel rods from a model coupling heat transfer and oxygen diffusion},
author = {Mihaila, Bogden and Zubelewicz, Aleksander and Stan, Marius and Ramirez, Juan},
abstractNote = {We study the thermal expansion of UO{sub 2+x} nuclear fuel rod in the context of a model coupling heat transfer and oxygen diffusion discussed previously by J.C. Ramirez, M. Stan and P. Cristea [J. Nucl. Mat. 359 (2006) 174]. We report results of simulations performed for steady-state and time-dependent regimes in one-dimensional configurations. A variety of initial- and boundary-value scenarios are considered. We use material properties obtained from previously published correlations or from analysis of previously published data. All simulations were performed using the commercial code COMSOL Multiphysics{sup TM} and are readily extendable to include multidimensional effects.},
doi = {},
journal = {J. Nuel.Mat},
number = ,
volume = ,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 2008},
month = {Tue Jan 01 00:00:00 EST 2008}
}
  • The simulation of nuclear reactor fuel performance involves complex thermomechanical processes between fuel pellets, made of fissile material, and the protective cladding barrier that surrounds the pellets. This paper examines asubset of phenomena that are important in the development of a predictive capability for fuel performance calculations, focusing on thermomechanics and diffusion within UO2 fuel pellets. In this study, correlations from the literature are used for thermal conductivity, specific heat, and oxygen diffusion. This study develops a three dimensional thermomechanical model fully-coupled to an oxygen diffusion model. Both steady state and transient results are examined to compare this three dimensionalmore » model with the literature. Further, this equation system is solved in a parallel, fully-coupled, fully-implicit manner using a preconditioned Jacobian-free Newton Krylov method. Numerical results are presented to explore the efficacy of this approach for examining selected fuel performance problems. INL’s BISON fuels performance code is used to perform this analysis.« less
  • Based on density functional theory (DFT) and empirical potential calculations, the diffusivity of fission gas atoms (Xe) in UO2 nuclear fuel has been calculated for a range of non-stoichiometry (i.e. UO2x), under both out-of-pile (no irradiation) and in-pile (irradiation) conditions. This was achieved by first deriving expressions for the activation energy that account for the type of trap site that the fission gas atoms occupy, which includes the corresponding type of mobile cluster, the charge state of these defects and the chemistry acting as boundary condition. In the next step DFT calculations were used to estimate migration barriers and internalmore » energy contributions to the thermodynamic properties and calculations based on empirical potentials were used to estimate defect formation and migration entropies (i.e. pre-exponentials). The diffusivities calculated for out-of-pile conditions as function of the UO2x nonstoichiometrywere used to validate the accuracy of the diffusion models and the DFT calculations against available experimental data. The Xe diffusivity is predicted to depend strongly on the UO2x non-stoichiometry due to a combination of changes in the preferred Xe trap site and in the concentration of uranium vacancies enabling Xe diffusion, which is consistent with experiments. After establishing the validity of the modeling approach, it was used for studying Xe diffusion under in-pile conditions, for which experimental data is very scarce. The radiation-enhanced Xe diffusivity is compared to existing empirical models. Finally, the predicted fission gas diffusion rates were implemented in the BISON fuel performance code and fission gas release from a Risø fuel rod irradiation experiment was simulated. 2014 Elsevier B.V. All rights« less
  • Quantum-mechanical techniques were used to determine the charge distribution of uranium atoms in UO2+x (x ≤ 0.25) and to calculate activation-energy barriers to oxygen diffusion. Upon optimization, the reduction in unit-cell volume relative to UO2, and the shortest and bond-lengths (0.22 and 0.24 nm, respectively) are in good agreement with experimental data. The addition of interstitial oxygen to the unoccupied cubic sites in the UO2 structure deflects two nearest-neighbor oxygen atoms along the body diagonal of uranium-occupied cubic sites, creating lattice oxygen defects. In (1×1×2) supercells, the partial oxidation of two U4+ atoms is observed for every interstitial oxygen addedmore » to the structure, consistent with previous quantum-mechanical studies. Results favor the stabilization of two U5+ over one U6+ in UO2+x. Calculated activation energies (2.06-2.73 eV) and diffusion rates for oxygen in UO2+x support the idea that defect clusters likely play an increasingly important role as oxidation proceeds.« less