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Formation of hyperstoichiometric uranium dioxide, UO2+x, derived from the fluorite structure was investigated by means of density functional theory (DFT) calculations. Oxidation was modeled by adding oxygen atoms to UO2 fluorite supercells. For each compound ab initio molecular dynamics simulations were performed to allow the ions to optimize their local(More)
Fuel retention, a crucial issue for next step devices, is assessed in present tokamaks using two methods : particle balance performed during shots and post mortem analysis carried out during shutdowns between experimental campaigns. Post mortem analysis generally gives lower estimates of fuel retention than particle balance. In order to understand the(More)
In a pretest-posttest design with two matched control groups, 86 first-graders screened as vulnerable to academic failure and behavioral decompensation were each assigned to one of three groups: (1) channel-specific perceptual stimulation, (2) regular academic tutoring (contact controls), or (3) no contact. On most measures, including perceptual and(More)
The aim of the present work is to introduce a thermodynamic model to describe the growth of an oxide layer on a metallic substrate. More precisely, this paper offers a study of oxygen dissolution into a solid, and its consequences on the apparition of mechanical stresses. They strongly influence the oxidation processes and may be, in some materials,(More)
The oxidation reaction of UO(2) into U(3)O(8) is studied as a function of the crystalline distortion of interstitial oxygen clusters, named cuboctahedra, which appear in U(4)O(9) and U(3)O(7) intermediate phases. For that purpose, the refinement of α-U(4)O(9) was performed because this phase undergoes a trigonal distortion from cubic β-U(4)O(9) when the(More)
In this article, we review our last advances on the Raman spectroscopy characterization of irradiated and/or leached UO<sub>2</sub>, PuO<sub>2</sub> and (U,Pu)O<sub>2</sub> samples. For this, three original Raman setups dedicated to the study of nuclear materials were involved. In all cases, irradiation was observed inducing the appearance of Raman defect(More)
Cracking and spalling are known to occur during the oxidation of UO2. However, these phenomena are not considered by the existing kinetic models of the oxidation of UO2 into U3O8. In this study the oxidation of UO2 samples of various sizes from the single crystal to nanopowders, has been followed by isothermal and isobaric thermogravimetry, environmental(More)
To some extent, rare-earth-doped UO(2) is representative of an irradiated nuclear fuel. The two phases we observed previously in neodymium-doped UO(2) are now interpreted as the existence of a miscibility gap in the U-Nd-O phase diagram using new results obtained with Raman spectroscopy. Extrapolating the miscibility gap in the U-Nd-O phase diagram to(More)
Cracking is observed when a UO2 single crystal is oxidised in air. Previous studies led to the hypothesis thatcracking occurs once a critical depth of U3O7 oxidised layer is reached. We present some μLaue X-Ray diffraction results, which evidence that the U3O7 layer, grown by topotaxy on UO2, is made of domains with different crystalline orientations. This(More)