0000000000255906
AUTHOR
Gianguido Baldinozzi
ChemInform Abstract: Neutron Diffraction Study of the in situ Oxidation of UO2.
This paper discusses uranium oxide crystal structure modifications that are observed during the low-temperature oxidation which transforms UO2 into U3O8. The symmetries and the structural parameters of UO2, β-U4O9, β-U3O7, and U3O8 were determined by refining neutron diffraction patterns on pure single-phase samples. Neutron diffraction patterns were also collected during the in situ oxidation of powder samples at 483 K. The lattice parameters and relative ratios of the four pure phases were measured during the progression of the isothermal oxidation. The transformation of UO2 into U3O8 involves a complex modification of the oxygen sublattice and the onset of complex superstructures for U4O…
On the origin of the sigmoid shape in the UO2 oxidation weight gain curves
International audience; 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 scanning electron microscopy and in situ X-ray diffraction at temperatures ranging from 250 to 370°C in air. It has been shown that cracking occurs once a critical layer thickness of intermediate oxide has been reached, which corresponds to the beginning of the sigmoid kinetic curve. Cracking contribution to the sigm…
Synchrotron diffraction study of the isothermal oxidation of uranium dioxide at 250°C
ABSTRACTThe structural evolution of UO2 during its oxidation to U3O8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases that are likely to appear during the long-term storage of spent nuclear fuel. Our results are in disagreement with the literature in which the existence of an intermediate cubic phase is not reported. Instead, an α-U3O7 tetragonal phase (c/a < 1) was mentioned but not definitively observed. These previous interpretations may have been the result of poor instrumental resolution.
Contribution of the synchrotron diffraction study of the oxidation of uranium dioxide at 250○C
The structural evolution of UO 2 during its oxidation into U 3 O 8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases which are likely to appear during a long term storage of used nuclear fuel. Our results are in disagreement with the literature where the existence of the secondary cubic phase is not reported, and an α-U 3 O 7 tetragonal phase (c/a < 1) is also mentioned but definitely not observed. These previous interpretations are possibly due to a poor instrumental resolution, inducing a sensible broadening of the diffraction peaks. Particularly, the fact that the instrumental resolution…
Neutron Diffraction Study of the in Situ Oxidation of UO2
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 diffraction patterns were also collected during the in situ oxidation of powder samples at 483 K. The lattice parameters and relative ratios of the four pure phases were measured during the progression of the isothermal oxidation. The transformation of UO(2) into U(3)O(8) involves a complex modification of the oxygen sublattice and the onset of…