Phase analysis of uranium oxides after reaction with stainless steel components and ZrO2 at high temperature by XRD, XAFS, and SEM/EDX

Tilting and Distortion in Rutile-Related Mixed Metal Ternary Uranium Oxides: A Structural, Spectroscopic, and Theoretical Investigation

“…The A UO 4 oxides have been shown to have the ability to host a variety of oxidation states of uranium. ,,, Previously, it had been assumed that only a specific structural type could host a specific oxidation state of uranium. However, our recent study of α-NiUO 4 demonstrated that despite being isostructural to CrU 5+ O 4 and FeU 5+ O 4 , ,, α-NiUO 4 contains hexavalent uranium .…”

“…Uranium oxides are known to display a panoply of structures and properties, in part due to the unique behavior of electrons in the 5f orbitals. − It has been of long-standing interest, and is of fundamental importance for the disposal of spent nuclear fuel (SNF), to examine the potential phase formation that may occur between fuel components, fission daughters, and near-field elements as these may impact the planning, assessment, and eventual repository operations. The A UO 4 monouranates ( A = divalent or trivalent cation) are a family of ternary uranium oxides relevant to nuclear waste forms − and also uranium mineral science. , Despite knowledge of them dating back to the Manhattan Project represented by Zachariasen’s pioneering X-ray studies of rhombohedral CaUO 4 and α-SrUO 4 , finer details of their chemical behavior are only gradually being unravelled. ,− This is exemplified by recent studies of α-SrUO 4 and CaUO 4 , , demonstrating their remarkable, and so far unique, symmetry lowering, defect ordering phase transformations with heating. That these phase transformations are apparently only observed in ternary uranium oxide compounds was attributed to the unique chemistry of uranium and in particular the importance of the collinear uranyl group, [OUO] 2+ .…”

Multimodal X-ray microanalysis of a UFeO4: evidence for the environmental stability of ternary U(v) oxides from depleted uranium munitions testing

“…Studies of the UO 2 -Fe 2 O 3 -ZrO 2 ternary phase diagram, under conditions relevant to severe nuclear power plant accidents, and Fukushima Daiichi in particular, demonstrate the formation of UFeO 4 . 47,48 The evidence presented here for the long term environmental stability of UFeO 4 , may therefore be of considerable importance in predicting the evolution of hot fuel particles in the environment.…”

“…Ternary compounds in the U-Fe-O system are of interest in the interaction of uranium wastes with iron oxides 3 and as a component of corium in severe nuclear power plant accidents. 4,5 Iron is ubiquitous in structural components of nuclear reactor systems, and in particular, some modern nuclear reactor designs employ hematite as a sacricial barrier in core catcher systems. 6 Compounds of Fe and U have also been previously described as minority phases in some hot particles.…”

Distribution of studtite and metastudtite generated on the surface of U3O8: application of Raman imaging technique to uranium compound

“…In the present study, we used the Raman imaging technique and successfully demonstrated the distribution data of the two types of uranyl peroxides formed in microscopic areas on the surface of a U 3 O 8 pellet. U 3 O 8 was selected as the starting material because it has been unclear whether the uranyl peroxides were generated from U 3 O 8 , although U 3 O 8 is a key component generated from UO 2 in oxidized conditions [17]. From the distribution data, we discussed some aspects of the generation and distribution of the two uranyl peroxides on U 3 O 8 .…”