Learn More
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)
This paper discusses uranium oxide crystal structure modifications that are observed during the low-temperature oxidation which transforms UO(2) into U(3)O(8). The symmetries and the structural parameters of UO(2), beta-U(4)O(9), beta-U(3)O(7), and U(3)O(8) were determined by refining neutron diffraction patterns on pure single-phase samples. Neutron(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)
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)
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)
The crystal structure of U4O9 remains an enigma because of its differences with U(4+) and U(5+) coordination polyhedral mixtures, as shown in the XANES experimental results. To better understand this crystal structure, its diffraction pattern was measured at seven different temperatures using neutron diffraction before being independently refined by(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)
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)
Up to now, uranium dioxide, the most used nuclear fuel, was said to have a Fm3̅m crystalline structure from 30 to 3000 K, and its behavior was modeled under this assumption. However, recently X-ray diffraction experiments provided atomic pair-distribution functions of UO2, in which UO distance was shorter than the expected value for the Fm3̅m space group.(More)