Uranium trioxide and the UO3 hydrates

Wheeler, V.J.; Dell, R.M.; Wait, E.

doi:10.1016/0022-1902(64)80007-5

Cited by 70 publications

(47 citation statements)

References 29 publications

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“…Thus far, no mechanism for dehydration has been proposed. The intermediate amorphous phase forming during the first transition (studtite → metastudtite), observed in previous studies (2,(19)(20)(21)(22)(23)(24), has not been well investigated. Its identity and following intermediate phases, especially regarding structure, remain unclear.…”

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confidence: 91%

“…This or a similar amorphous phase was identified as different compounds from various studies (2,(19)(20)(21)(22)(23). Using both evolved gas and TG analysis (Table 1), we determined it to be amorphous UO 3 ·nH 2 O (am-UO 3 ·nH 2 O), which is consistent with previous thermal decomposition experiments (19)(20)(21)23). From 240°C to 500°C, TG and DSC indicate loss of water from am-UO 3 ·nH 2 O to amorphous UO 3 (am-UO 3 ) composition before crystallization, as can be seen in the XRD pattern of sample retrieved at 530°C (Fig.…”

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confidence: 99%

“…3) just before the first exothermic peak. The subsequent exothermic peak reveals the energy released during the crystallization, which is accompanied by loss of oxygen and generating UO 2.9 , an orthorhombic phase (20) that resembles the structure of U 3 O 8 . The sample retrieved from 580°C was α-UO 2.9 ( Fig.…”

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confidence: 99%

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Energetics of metastudtite and implications for nuclear waste alteration

Guo

Ushakov

Labs

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Metastudtite, (UO 2 )O 2 (H 2 O) 2 , is one of two known natural peroxide minerals, but little is established about its thermodynamic stability. In this work, its standard enthalpy of formation, −1,779.6 ± 1.9 kJ/mol, was obtained by high temperature oxide melt drop solution calorimetry. Decomposition of synthetic metastudtite was characterized by thermogravimetry and differential scanning calorimetry (DSC) with ex situ X-ray diffraction analysis. Four decomposition steps were observed in oxygen atmosphere: water loss around 220°C associated with an endothermic heat effect accompanied by amorphization; another water loss from 400°C to 530°C; oxygen loss from amorphous UO 3 to crystallize orthorhombic α-UO 2.9 ; and reduction to crystalline U 3 O 8 . This detailed characterization allowed calculation of formation enthalpy from heat effects on decomposition measured by DSC and by transposed temperature drop calorimetry, and both these values agree with that from drop solution calorimetry. The data explain the irreversible transformation from studtite to metastudtite, the conditions under which metastudtite may form, and its significant role in the oxidation, corrosion, and dissolution of nuclear fuel in contact with water. Metastudtite is the main natural peroxide mineral (1) due to the irreversible dehydration of studtite (2). Both these phases may be found in spent nuclear fuel exposed to water (3-5). Burns et al. (6), by single crystal diffraction of a natural sample, determined the crystal structure of studtite to be monoclinic with space group C2/c. The structure consists of edge-sharing UO 8 -polyhedra chains. The water molecules are located on two different positions between these chains. Although there are different, yet very similar, models for metastudtite, thus far no structure has been determined (7,8). It is highly probable that metastudtite, like studtite, consists of chains of edge-sharing UO 8 polyhedra with the water molecules located between the chains. To better depict the bonding situation and the different oxygen atoms, it is proposed to write the sum formulas as (UO 2 )(O 2 )(H 2 O) 2 ·2H 2 O for studtite and (UO 2 )(O 2 )(H 2 O) 2 for metastudtite [in analogy to Burns et al. (6)].Studtite and other polyoxouranylates have a potentially important role as alteration phases in geological repositories for nuclear waste, specifically regarding the interactions of nuclear waste with the aqueous environment (9, 10). They have also been proposed as corrosion products in sea water after the FukushimaDaiichi nuclear plant accident (10-12).In a nuclear waste repository, the high alpha dosage will be the dominant factor after the first thousand years of storage (13). In combination with groundwater, the alpha radiation will lead to formation of H 2 O 2 (3, 4, 9, 14). These very localized oxidative conditions could trigger the genesis of studtite or metastudtite even if the overall conditions are reducing (14). The formation of metastudtite on UO 2 samples as a direct effect of alpha radiolysis of water w...

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confidence: 91%

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confidence: 99%

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Energetics of metastudtite and implications for nuclear waste alteration

Guo

Ushakov

Labs

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…The formation of U03 from UO3-based hydrates was reported by Wheeler et al (1964), who performed an extensive review of the (then-current) literature and documented three forms: U03-2H20, U03.H20, and uO3-0.5H20. In the present study, the mineral phase, "paraschoepite," was identified, with a corresponding composition identified as UO2.86.1.5H20.…”

Section: Phases Identifiedmentioning

confidence: 92%

“…However, the existence of these modified species has since been determined. Wheeler et al (1964) also reported information on the decomposition of the hydrates. They did not report details of the reaction mechanisms because they simply prepared mixtures of various hydrates to determine what phases of oxide would be formed by thermal decomposition.…”

Section: Phases Identifiedmentioning

confidence: 99%

Examination of the surface coating removed from K-East Basin fuel elements

Abrefah¹,

Marschman²,

Jenson³

1998

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Summary *This report provides the results of studies conducted on coatings discovered on the surfaces of some N-Reactor spent nuclear fuel (SNF) elements stored at the Hanford K-East Basin. These elements had been removed from the canisters and visually examined in-basin during FY 1996 as part of a series of characterization tests. The characterization tests are being performed to support the Integrated Process Strategy developed to package, dry, transport, and store the SNF in an interim storage facility on the Hanford Site.Samples of coating materials were removed from K-East canister elements 2350E and 2540E, which had been sent, along with nine other elements, to the Postirradiation Testing Laboratory (327 Building) for further characterization following the in-basin examinations. These coating samples were evaluated by Pacific Northwest National Laboratory using various analytical methods. This report is part of the overall studies to determine the drying behavior of corrosion products associated with the K-Basin fuel elements.Altogether, five samples of coating materials were analyzed. These samples were identified by X-ray diffraction analysis to primarily be composed of uranium oxides and oxyhydrates. Scanning electron microscope analysis showed these samples to consist of small needles or agglomerates composed of smaller particulates and needles. This composition indicates the coatings may be formed as part of a nucleation and precipitation process. Thermogravimetric analysis combined with the total weight of material recovered from some of the elements yielded a water-content-per-surface-area-of-fuel estimate of 6-1 O4 mol water/cm2. These analyses suggest that hydration of the coating materials could be an additional source of moisture in the Multi-Canister Overpacks being used to contain the fuel for storage.iii E Acknowledgment

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