Pneumatic irradiation facilities are used for neutron activation analysis, materials testing, electronics hardening, and radioisotope production. The application of these facilities can benefit from a greater understa...
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Using density functional theory, we examine a recently discovered structure for di-interstitial oxygen clusters in UO2+x in which three oxygen ions share one lattice site. This di-interstitial cluster exhibits a fast ...
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Using density functional theory, we examine a recently discovered structure for di-interstitial oxygen clusters in UO2+x in which three oxygen ions share one lattice site. This di-interstitial cluster exhibits a fast diffusion pathway; the migration barrier for these clusters is approximately half of that for mono-interstitials. Using kinetic Monte Carlo, we calculate the diffusivity of oxygen with and without the di-interstitial mechanism as a function of x and find that oxygen transport is significantly increased for higher values of x when the di-interstitial mechanism is included, agreeing much more closely with experimental data. These results emphasize the importance of clustering phenomena in UO2+x and have implications for the evolution of UO2+x.
Actinide dioxides derived from the AO2 fluorite lattice are of high technological relevance due to their application in nuclear reactor fuels. In this paper we use density functional theory calculations to study the o...
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Actinide dioxides derived from the AO2 fluorite lattice are of high technological relevance due to their application in nuclear reactor fuels. In this paper we use density functional theory calculations to study the oxidation of uranium, neptunium and plutonium dioxides, AO2 (A=U, Np, or Pu), in O2 and O2/H2O environments. We pay particular attention to the formation of oxygen clusters (cooperativity) in AO2+x and how this phenomenon governs oxidation thermodynamics and the development of ordered A4O9 compounds. The so-called split di-interstitial, composed of two nearest-neighbor octahedral oxygen interstitials that dislocate one regular fluorite lattice oxygen ion to form a cluster of triangular geometry, is predicted to be the fundamental building block of the most stable cluster configurations. We also identify how the formation of oxygen defect clusters and the degree of oxidation in AO2+x are both governed by the ability of the O 2p orbitals of the interstitial-like (+x) ions to hybridize with regular fluorite lattice ions.
The DLRs and Carmen course management software have enabled an NPP Systems and Operations Course to be successfully taught as a single class to a diverse audience from five different schools with different academic ca...
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The DLRs and Carmen course management software have enabled an NPP Systems and Operations Course to be successfully taught as a single class to a diverse audience from five different schools with different academic calendars, enabling a critical mass of students to come together for a course that otherwise could not be taught. The hardware and software environments have proven to be user friendly and easy to learn by both instructors and students.
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