Hydration of α-UO₃following storage under controlled conditions of temperature and relative humidity

Abstract

Experimental measurements and theoretical evaluation of changes in chemical speciation of α-UO3 using XRD, EXAFS, TGA, and DFT calculations.

Progress in Uranium Chemistry: Driving Advances in Front-End Nuclear Fuel Cycle Forensics

“…One other UOC chemical form, UO 3 , was recently studied by Wilkerson et al to understand the effect of aging UO 3 under controlled humidity and temperature conditions for several years. 58 They used p-XRD and EXAFS to determine changes in chemical speciation in α-UO 3 samples stored in cool and dry (5 °C, 25% RH), cool and humid (5 °C, 97% RH), warm and dry (37 °C, 15% RH), or warm and humid (37 °C, 89% RH) conditions. After 14 months of storage, schoepite (UO 3 •xH 2 O) compounds were present in each α-UO 3 sample, except for the sample stored in cool and dry conditions.…”

“…Recent research has also investigated elemental and chemical impurities present in process samples of uranium compounds, also with a focus of discerning process history as well as the origin of the uranium. − ,,,− For example, the concentrations of rare-earth elements (REEs) have been found to be potentially useful for identifying the origin of UOCs . Other research has focused on understanding the degradation of uranium compounds, particularly under environmental conditions. − These efforts are important for nuclear forensics investigations of aged materials or samples exposed to the environment. For instance, various UOCs stored in controlled relative humidity (RH) and temperature conditions have undergone chemical reactions, converting them to different uranium compounds. ,− One final focus area has been developing improved or new analytical techniques for probing various key uranium compounds. − For example, laser-induced breakdown spectroscopy (LIBS), which can be packaged in a field-deployable form factor, has been studied as a possible technique to rapidly identify various uranium oxides and UO 2 F 2 . , Overall, the significance of the recent research and the growing importance of nuclear forensics is evident in the proposal and establishment of Nuclear Proliferomics, a field of study focused on building comprehensive databases of nuclear materials’ properties that could be leveraged through various data analytics and machine-learning techniques to advance nuclear forensics analyses …”

Characterization of Uranyl Coordinated by Equatorial Oxygen: Oxo in UO3 versus Oxyl in UO3+

“…31,32 A key consideration for UO3(s) behavior is kinetics for transformation of its hydrate UO3(H2O) to hydroxide UO2(OH)2. [33][34][35][36][37][38][39] Hydroxides such as found in minerals are thermodynamically more stable than hydrates of uranium trioxide, 38 but mechanisms of the hydrate-to-hydroxide transformations on timescales shorter than geological and thus more relevant to material storage and processing are poorly understood. 39 Although uranyl coordination chemistry is studied primarily in condensed phases, gasphase complexes reveal intrinsic character, such as Oyl reactivity, unperturbed by solvent or lattice.…”

“…[33][34][35][36][37][38][39] Hydroxides such as found in minerals are thermodynamically more stable than hydrates of uranium trioxide, 38 but mechanisms of the hydrate-to-hydroxide transformations on timescales shorter than geological and thus more relevant to material storage and processing are poorly understood. 39 Although uranyl coordination chemistry is studied primarily in condensed phases, gasphase complexes reveal intrinsic character, such as Oyl reactivity, unperturbed by solvent or lattice. 5 Whereas hydration/hydrolysis of solid UO3 is an inherently complex phenomenon, the analogous bimolecular association of UO3 and H2O is relatively straightforward, yielding a discrete hydrate, UO3(H2O), or hydroxide, UO2(OH)2.…”

“…Solid uranium trioxide, UO 3 (s) , exhibits six allotropes and is important in nuclear fuel cycles. − Although the allotropes are not simple assemblies of molecular UO 3 , the structures do exhibit characteristics of uranyl moieties equatorially coordinated by oxygen. , Hydration of solid UO 3 under ambient conditions ultimately forms minerals such as shoepite. , A key consideration for UO 3 (s) behavior is kinetics for transformation of its hydrate UO 3 (H 2 O) to hydroxide UO 2 (OH) 2 . − Hydroxides such as found in minerals are thermodynamically more stable than hydrates of uranium trioxide, but mechanisms of the hydrate-to-hydroxide transformations on time scales shorter than geological and thus more relevant to material storage and processing are poorly understood …”