Molten uranium dioxide structure and dynamics

Abstract

diffusion remains below 10 −4 nm 2 s −1. In the liquid state at 3270 K, the rates of U and O diffusion are of similar magnitude (3.7 versus 9.3 nm 2 s −1). Manara et al. measured a melting slope (dT m /dP) that is a factor 1.5 to 2 steeper than expected from the recommended volume change on melting and enthalpy of fusion values (11, 16). The rapid O exchange in these MD models results in a relatively low enthalpy of fusion, consistent with a relatively steep melting slope. Using pressure , an 8-coordinated UO 2 melt can be simulated at a number density of 0.074 Å −3. The 8-coordinated melt has U and O diffusion rates slower by a factor of 3 (1.2 and 3.8 nm 2 s −1) than the low-coordinated melt, demonstrating the strong effect of local structure on the physical properties of this melt. The Andrade theory, for example, is often used to predict melt viscosity but assumes that the melt structure closely resembles that of the solid (17, 18). Portions of the hot solid and liquid UO 2 MD simulations illustrate the large oxygen disorder above the lambda transition and the different UO 6,7 coordination species that predominate in the melt (Fig. 3C). The structure and optimized interatomic potentials for UO 2 allow for accurate atomistic multiscale modeling. The x-ray data are important as an end-member benchmark for models of multicomponent systems, including corium melts and high-level waste glasses (11). (6212), 987-991. 346 Science , this issue p. 987 Science mice could prove valuable for preliminary screens of candidate therapeutics and vaccines. virus was associated with distinct genetic profiles in inflammation, blood coagulation, and vascular function. This panel of series of painstaking experiments performed under stringent biosafety conditions. Resistance and susceptibility to Ebola tested the effects of Ebola virus in mice with defined genetic backgrounds in a et al. as those of humans. Rasmussen Apart from monkeys, there are no animal models available that show the same symptoms of Ebola virus infection Variety of Ebola symptoms in mice ARTICLE TOOLS

Electrochemical Study of a Pendant Molten Alumina Droplet and Its Application for Thermodynamic Property Measurements of Al-Ir

“…While these methods are currently preferred for measuring structure, 10,11,25,26 total conductivity, 21 density, viscosity and surface tension 24,27 or even integral thermodynamic properties, 28 the sample size is necessarily small (1-4 mm) and each method is limited to their respective subset of compatible atmospheres (e.g. vacuum only for electrostatic levitation).…”

Recent advances in identifying the structure of liquid and glassy oxide and chalcogenide materials under extreme conditions: a joint approach using diffraction and atomistic simulation

“…Figure 5 shows the temperature dependence of the X-ray pair-distribution function D X (r) ≡ 4 r G X (r) − 1 for UO 2 in both its crystalline solid and liquid phases, covering a temperature range of 1300-3270 K. On melting, there is a marked drop in the average U-O coordination number from 8 to 6.7 ± 0.5 and molecular dynamics simulations, made with pair-potentials that were refined using the diffraction results, show a distribution of U-centred oxygen polyhedra. The simulations predict a liquid state mobility for the chemical species that is higher than found from a model of the liquid in which there is no change to the U-O coordination number on melting [9]. Figure 5.…”

“…Accordingly, there has been much work on the atomic structure of levitated oxide liquids [6][7][8][9][10], and on the glasses synthesised from levitated liquids [6,10,11], using X-ray and neutron diffraction. Of the different levitation techniques that can be used [6], aerodynamic levitation with laser heating is the most popular because the instrumentation is compact and works well for a wide variety of materials.…”

“…Of the different levitation techniques that can be used [6], aerodynamic levitation with laser heating is the most popular because the instrumentation is compact and works well for a wide variety of materials. We will focus on recent work to uncover the structure of the high-temperature oxide liquids Al 2 O 3 [7], ZrO 2 [8] and UO 2 [9] as well as the structure of materials in the fragile glass-forming system CaO-Al 2 O 3 in their high-temperature liquid and/or glassy forms [10][11][12]. Previous work on oxide liquids is reviewed elsewhere [6].…”

“…Recently, it has proved possible, however, to tackle this problem using aerodynamic levitation with laser heating and XRD [9]. Figure 5 shows the temperature dependence of the X-ray pair-distribution function D X (r) ≡ 4 r G X (r) − 1 for UO 2 in both its crystalline solid and liquid phases, covering a temperature range of 1300-3270 K. On melting, there is a marked drop in the average U-O coordination number from 8 to 6.7 ± 0.5 and molecular dynamics simulations, made with pair-potentials that were refined using the diffraction results, show a distribution of U-centred oxygen polyhedra.…”