Milestone report: The simulation of radiation driven gas diffusion in UO₂ at low temperature

Technical Report · Mon Oct 24 00:00:00 EDT 2016

DOI:https://doi.org/10.2172/1330173· OSTI ID:1330173

Cooper, Michael William ^[1]; Kuganathan, Navaratnarajah ^[2]; Burr, Patrick A ^[3]; Rushton, Michael J. ^[2]; Grimes, Robin W ^[2]; Turbull, James Anthony ^[4]; Stanek, Christopher Richard ^[1]; Andersson, Anders David ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Imperial College, London (United Kingdom)
3. Univ. of New South Wales (Australia)
4. Independent Consultant (United Kingdom)

Below 1000 K it is thought that fission gas diffusion in nuclear fuel during irradiation occurs through atomic mixing due to radiation damage. This is an important process for nuclear reactor performance as it affects fission gas release, particularly from the periphery of the pellet where such temperatures are normal. Here we present a molecular dynamics study of Xe and Kr diffusion due to irradiation. Thermal spikes and cascades have been used to study the electronic stopping and ballistic phases of damage, respectively. Our results predict that O and Kr exhibit the greatest diffusivity and U the least, while Xe lies in between. It is concluded that the ballistic phase does not sufficiently account for the experimentally observed diffusion. Preliminary thermal spike calculations indicate that the electronic stopping phase generates greater fission gas displacement than the ballistic phase, although further calculation must be carried out to confirm this. A good description of the system by the empirical potentials is important over the very wide temperatures induced during thermal spike and damage cascade simulations. This has motivated the development of a parameter set for gas-actinide and gas-oxygen interactions that is complementary for use with a recent many-body potential set. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO₂, ThO₂, UO₂ and PuO₂. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matching to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT binding energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO₂, ThO₂, UO₂ and PuO₂, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO₂ as well as advanced MOX fuels.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 1330173
• Report Number(s): LA-UR-16-23474; TRN: US1700436
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
22 GENERAL STUDIES OF NUCLEAR REACTORS
URANIUM DIOXIDE
MIXED OXIDE FUELS
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 1000-4000 K
TEMPERATURE RANGE OVER 4000 K
PLUTONIUM OXIDES
FISSION PRODUCTS
DENSITY FUNCTIONAL METHOD
CERIUM OXIDES
THORIUM OXIDES
SOLID SOLUTIONS
MOLECULAR DYNAMICS METHOD
DIFFUSION
POTENTIALS
COMPUTERIZED SIMULATION
THERMAL SPIKES
OXYGEN
BINDING ENERGY
IRRADIATION
FISSION PRODUCT RELEASE
MANY-BODY PROBLEM
RADIATION EFFECTS
FUEL PELLETS
KRYPTON
XENON
URANIUM