Atomistic simulations of the small xenon bubble behavior in U–Mo alloy

Atomistic simulations of thermodynamic properties of Xe gas bubbles in U10Mo fuels

“…When the gas bubble radius is larger than 1.2nm(up to the largest radius of 1.5nm that the simulations reach), the pressure and Xe concentration are almost constants, namely at about 6.05~6.35GPaand 0.49~0.50, respectively. (Insert Figure 3. here) Predicted gas bubble radius, pressure, and Xe concentration inside the bubble as a function ofthe number of Xe atoms Xe N inside the bubble.The pressure inside a Xe gas bubble in U10Mo alloys was previously simulated by Xiao et al[27]using the same EAM potential[1]. The parameters used in their simulations, such as temperature T=500K, initial void sizeR 0 = 0.8 nm, MD time step 1 fs, and atomic potential, are the same as those for the case with small initial gas bubble radius in our simulations.…”

“…The properties of defectsin bcc U single crystals have been investigated via experiments [4,[11][12][13], density functional theory (DFT) [14][15][16][17][18], and molecular dynamics (MD) method [1,16,19,20].The results show that 1) Xe is stableas a substitutional defect, and Xe migrates through vacancy-assisted mechanisms, presumably as a complex consisting of one Xe and two vacancies (XeV 2 complex), 2) the dumbbell configurations of U interstitials along the [100] or [110] direction are energetically favored, and 3) the migration barrier of U interstitials is about 0.1 eV, which is much smaller than that of vacancies (0.5eV).The defect generation and spatial distribution during cascades in bcc U were simulated using MD methods [21,22].The results show that most of the surviving interstitials form a [100] or [110] dumbbell.Almost all the interstitials remain isolated, while vacancies tend to cluster into polyhedral voids [22].The equation of state (EOS) of the Xe gas phase has been examined by experiments [23][24][25] and atomistic simulations [26]. Very recently, Xiao et al simulated the pressure inside Xe bubbles with different Xe concentrations in bcc U10Mo alloys [27]. In their simulations, a bubble was introduced into the simulation cell by adding a certain number of Xe atoms into a given void.…”

“…The pressure drop in their simulations is about 7GPa, which is much larger than the 2GPaobserved in our simulations.The value of pressure after it becomes constant is about 4GPa, which is lower than the 6GPa predicted in our simulations.As we can imagine, an unphysically high initial Xe concentration inside a void may drive the system far away from equilibrium. As a result, an unrealisticallylarge lattice distortion and amorphization around the bubble may happen, which would affect the pressure inside the bubble.Figure 2shows the dislocation emission and deformation twinning that are observed in our simulations, while they are not observed around the overpressured gas bubble in their simulations.Therefore, the overestimated pressure drop and underestimated equilibrium pressure in Ref[27]are likely the consequences of an unrealistic MD simulation process.To examine the effect of fcc gas bubble superlattice structure on pressure and Xe concentration, anfcc gas bubble superlatticewith a similar bubble size (1~3 nmin diameter) and superlattice constant ( ) as observed in irradiated U10Mo fuels was considered. The same simulation process described above was employed.The results are plotted inFigure 4togetherwith the results from the scsuperlattice simulations for comparison.…”

Xenon Diffusion Mechanism and Xenon Bubble Nucleation and Growth Behaviors in Molybdenum via Molecular Dynamics Simulations

“…Meanwhile, the calculated vacancy and SIA formation energies in U and Mo agree well with the ab initio calculation results, which proved that the potential may be used to predict the defect behaviors. Xiao H. [22] and Hu S. [23] also used this potential in their simulations. Consequently, it is believed that the potential is suitable to be used for our simulation.…”

Effects of Zr doping on the surface energy and surface structure of UO2: Atomistic simulations

“…Knowledge of the surface energy and surface structure of a nuclear fuel is of importance for the understanding and prediction of the crystal morphologies, crystal growth rates, cleavage, pore shapes, strength, sintering, fracture behavior and the gas absorption [19][20][21][22][23]. Moreover, the surface energy is a significant parameter in the nucleation, growth, migration and coalescence of fission gas bubbles as well as the fission gas release in nuclear fuel [24,25].…”