Temperature‐dependent Variations of the Interface between UO₂ and Zr

Abstract

Temperature‐dependent variations of the interface between uranium dioxide and zirconium in UO2 ‐Zr systems were studied using X‐ray photoelectron spectroscopy. The surface of the uranium dioxide sample was oxidized to hyperstoichiometric UO 2+x composed of U(IV), U(V), and U(VI) valence states at room temperature, whereas UO2 consisting of the only U(IV) oxidation state appeared after annealing with zirconium. In the zirconium sample, its surface was spontaneously oxidized to ZrO2 at room temperature, whereas it was variously changed after heating the UO2 ‐Zr sample. Furthermore, we observed a molten product composed of α‐Zr(O), (U,Zr)O2 , and ZrO2 when a UO2 ‐Zr sample was fully melted.

Change of Composition in Metallic Fuel Slug of U–Zr Alloy from High‐Temperature Annealing

“…10 To minimize exposure to air, the sample annealed in the high vacuum system was quickly transferred into the Raman spectroscopy and XRD instrument. 12 The satellite peaks of U(VI) oxidation state are not clear in Figure 1(a) because the intensity of the primary peak is low, which is also in accordance with prior study. The spectra were acquired during 300 s exposure in the wavenumber ranges of 230-1050 cm −1 and 1050-1760 cm −1 .…”

“…The peaks U1 at 377.6 eV, U2 at 379.6 eV, and U3 at 381.0 eV are assigned to the U metal, U(IV) oxidation state, and U(VI) valence state, respectively, according to previous literature . Furthermore, the satellite peak of U 4f 5/2 associated with the U(IV) valence state is clearly visible at 397.2 eV (indicated by an arrow in Figure (a)), which is calculated by summing the main U 4f 7/2 binding energy (379.6 eV), the separation energy between U 4f 7/2 and U 4f 5/2 levels (10.9 eV), and the isolated energy between the main U 4f 5/2 and its satellite signals (6.7 eV) . The satellite peaks of U(VI) oxidation state are not clear in Figure (a) because the intensity of the primary peak is low, which is also in accordance with prior study .…”

“…Furthermore, the satellite peak of U 4f 5/2 associated with the U(IV) valence state is clearly visible at 397.2 eV (indicated by an arrow in Figure (a)), which is calculated by summing the main U 4f 7/2 binding energy (379.6 eV), the separation energy between U 4f 7/2 and U 4f 5/2 levels (10.9 eV), and the isolated energy between the main U 4f 5/2 and its satellite signals (6.7 eV) . The satellite peaks of U(VI) oxidation state are not clear in Figure (a) because the intensity of the primary peak is low, which is also in accordance with prior study . Therefore, we conclude that before annealing most of the uranium metal on the surface was oxidized to hyperstoichiometric UO 2+ x containing U(IV) and U(VI) oxidation states because of the exposure to air after fabrication.…”

“…9 All spectra were analyzed using a standard nonlinear least-squares fitting procedure with Voigt functions. [12][13][14] Furthermore, the satellite peak of U 4f 5/2 associated with the U(IV) valence state is clearly visible at 397.2 eV (indicated by an arrow in Figure 1(a)), which is calculated by summing the main U 4f 7/2 binding energy (379.6 eV), the separation energy between U 4f 7/2 and U 4f 5/2 levels (10.9 eV), and the isolated energy between the main U 4f 5/2 and its satellite signals (6.7 eV). The Raman spectra were measured by an ANDOR Shamrock SR303i Article Raman spectrometer (ANDOR, Belfast, UK) with a helium-neon laser of 632.8 nm wavelength operating at 8 mW.…”

“…The Raman spectra were measured by an ANDOR Shamrock SR303i Article Raman spectrometer (ANDOR, Belfast, UK) with a helium-neon laser of 632.8 nm wavelength operating at 8 mW. 12 Therefore, we conclude that before annealing most of the uranium metal on the surface was oxidized to hyperstoichiometric UO 2+x containing U(IV) and U(VI) oxidation states because of the exposure to air after fabrication. The laser was focused onto the sample using 50× uncoated objective lenses.…”