Simulation of uranium dioxide polymorphs and their phase transitions

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International audienceWe assess five empirical interatomic potentials in the approximation of rigid ions and pair interactions for the (U1−y,Puy)O solid solution. The assessment compares available experimental data and Fink's recommendation with simulations on: the structural, thermodynamics, and mechanical properties over the full range of plutonium composition, from pure UO2 to pure PuO2 and for temperatures ranging from 300 K to the melting point. The best results are obtained by potentials referred as Cooper and Potashnikov potentials. The first one reproduces more accurately recommendations for the thermodynamics and mechanical properties exhibiting ductile-like behaviour during crack propagation, while the second one gives brittle behaviour at low temperature

Section: Stress-strain Curvessupporting

confidence: 92%

Section: Stress-strain Curvesmentioning

confidence: 56%

Section: Stress-strain Curvesmentioning

confidence: 80%

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Assessment of empirical potential for MOX nuclear fuels and thermomechanical properties

Balboa

Brutzel

Chartier

et al. 2017

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“…We have further confirmed that our key results agree with those using the interionic potential developed by Basak et al [27] (see Appendix 2). While several potentials have been reported for simulating UO2 properties [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], our choice has been largely dictated by the ability of the potential to predict high temperature properties and transitions.…”

Section: Molecular Dynamics (Md) Simulationsmentioning

confidence: 99%

Disordering and dynamic self-organization in stoichiometric UO2 at high temperatures

Annamareddy

Eapen

2017

Using atomistic simulations and metrics from statistical mechanics we show that the oxygen anions in UO2 predominantly hop from one native (tetrahedral) lattice site to another, above a characteristic temperature Tα (~2000 K). Interestingly, we discover two types of disorder-the first one, which is a measure of the fraction of anions that are displaced from their native sites, portrays a monotonic increase with temperature and shows excellent conformity to neutron scattering data. The second metric demonstrates a dynamic clustering or self-organization behavior wherein the anions are spatially correlated to those with similar mobility. The dynamic self-organization, however, experiences a non-monotonic variation with temperature depicting a maximum near the Bredig or λ-transition. We further establish that the thermodynamic metric cp/T, which is equal to the rate of change of entropy with temperature, is a key thermodynamic indicator of the dynamic disorder among the oxygen anions.

“…Mechanical properties such as crack initiation and propagation on unirradiated UO 2 have already been assess via MD simulations using empirical potentials [16][17][18]. These simulations examined the strain-stress curves during crack propagation and reported the existence of phase transitions ahead from the crack tip from fluorite to scrutinyite-type or rutile-type structure.…”

Section: Introductionmentioning

confidence: 99%

Damage characterization of (U,Pu)O2 under irradiation by molecular dynamics simulations

Balboa

Brutzel

Chartier

et al. 2018

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Molecular dynamics simulations using two empirical potentials: Cooper and MOX-07 are carried out to assess the mechanical properties of U x Pu 1−x O 2 solid solution as a function of irradiation dose. The structural damage evolution with dose is modelled with the accumulation of Frenkel pairs method. The structural change follows classical steps with increasing dose: first accumulation of point defects that cluster and form dislocation loops which transform in turn to dislocation lines. Elastic properties such as the bulk modulus and the anisotropic factor via the Zener's ratio are evaluated for each steps. Overall, bulk moduli decrease with increasing dose while anisotropic factor behaviour depends on the potential used. It is also found that point defects play a major role in these evolution. Traction-separation curves used in cohesive zone models are also calculated for different irradiation doses. From these curves we extract the tensile strengths and the energy release rates as well as the fracture toughness. Fracture toughness is found to increase steadily with dose whereas tensile strengths displays v-shape curves which decreases for low doses and raises for high doses. For all these mechanical properties, point defects seem to play a major role while the impact of the dislocations is rather minor.