Alpha-radiolysis effects on UO2 alteration in water

Sattonnay, G.; Ardois, Christophe; Corbel, C.; Lucchini, Jean-François; Barthe, M.F.; Garrido, F.; Gosset, Dominique

doi:10.1016/s0022-3115(00)00714-5

Cited by 150 publications

(149 citation statements)

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“…Studtite was a major alteration phase of fuel-element claddings, and also occurred on the basin floor and in canister sludge (12). Studtite also formed on spent fuel in deionized water under laboratory conditions (13), and on UO 2 doped with alpha emitters or irradiated by an external source in water (2,(14)(15)(16)(17).Where seawater flow is relatively stagnant in the FukushimaDaiichi systems, peroxide will accumulate, it will increase corrosion rates of exposed UO 2 , and it will complex uranyl ions in solution. The seawater, with a pH of approximately 8, will provide abundant Na and lesser K to balance the charge of the resulting uranyl peroxide complexes that form in solution and in precipitates.…”

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confidence: 93%

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Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Armstrong

Nyman

Shvareva

et al. 2012

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

135

177

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The Fukushima-Daiichi nuclear accident brought together compromised irradiated fuel and large amounts of seawater in a high radiation field. Based on newly acquired thermochemical data for a series of uranyl peroxide compounds containing charge-balancing alkali cations, here we show that nanoscale cage clusters containing as many as 60 uranyl ions, bonded through peroxide and hydroxide bridges, are likely to form in solution or as precipitates under such conditions. These species will enhance the corrosion of the damaged fuel and, being thermodynamically stable and kinetically persistent in the absence of peroxide, they can potentially transport uranium over long distances.F ailed cooling systems in the reactors and spent fuel cooling ponds at the Fukushima-Daiichi nuclear power plants resulted in compromised irradiated fuel and release of radionuclides. Copious amounts of seawater were subsequently used to cool the fuel. The collocation of large quantities of damaged fuel, an intense radiation field, and massive amounts of seawater has created a highly heterogeneous and presumably rapidly evolving system that has the potential to release vast quantities of radionuclides to the environment. Currently, large quantities of contaminated water remain onsite (1), and presumably some has been released to the subsurface as well as to the Pacific Ocean.The fuel matrix at the Fukushima-Daiichi site is mainly UO 2 , whose behavior will largely dictate release of matrix-incorporated plutonium and various other radionuclides into water used as a coolant. The intense radiation field of the fuel will cause radiolysis of water and formation of peroxide (as well as other species) (2). Peroxide enhances the corrosion rate of UO 2 by oxidizing U (IV) to the much more soluble U(VI) that exists as the linear dioxo uranyl cation, ðUO 2 Þ 2þ . Peroxide strongly complexes uranyl (3), which increases its aqueous solubility under alkaline conditions.Simple uranyl peroxide complexes contain a single uranyl ion coordinated by as many as three peroxide groups that, each being bidentate, define the equatorial edges of hexagonal bipyramidal coordination polyhedra (4) (Fig. 1). These small complexes associate with counterions locally to balance charge in solution and readily crystallize as alkali metal salts (4-6). When peroxide bridges uranyl ions, the configuration is bent (7-9) and nanoscale cage clusters containing as many as 60 uranyl ions self-assemble in aqueous systems (10) (Fig. 1). These soluble clusters carry negative charges, are associated with counterions in solution, and can be crystallized. Under acidic conditions in deionized water, the combination of uranyl and peroxide causes the precipitation of studtite, ½ðUO 2 ÞðO 2 ÞðH 2 OÞ 2 ðH 2 OÞ 2 (11).Some insight into the geochemical interactions of uranium and peroxide that may occur in the Fukushima-Daiichi systems emerge from cases where deionized water, UO 2 , and ionizing radiation have been combined. Irradiated fuel was stored in the K-East Basins of the plutonium-productio...

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confidence: 93%

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confidence: 99%

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Armstrong

Nyman

Shvareva

et al. 2012

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

135

177

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“…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)(4)(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.…”

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confidence: 99%

“…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).…”

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confidence: 99%

“…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 was observed by Sattonay et al (3). Studtite and metastudtite were identified by Hanson et al (5) as the only secondary phases left in a 2-y corrosion experiment on spent nuclear fuel.…”

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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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The U₂₈ Nanosphere: What's Inside?

2011

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, and (X) containing the [UO2(O2)1.5]28 (U28) nanosphere are characterized by powder and single crystal XRD, and IR spectroscopy. (IV) and (X) are further characterized by 133 Cs NMR spectroscopy. While Cs + internal to the cluster remains inside when U28 is dissolved in a Na salt solution, the internal K + rapidly exchanges with Na + , providing new routes to other cluster topologies and compositions. (IV), (VI), and (X) crystallize in the monoclinic space group P21/m with Z = 2, and (VIII) crystallizes in the cubic space group I23 with Z = 2. -(NYMAN*, M.; RODRIGUEZ, M. A.; ALAM, T. M.; Eur.

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Alpha-radiolysis effects on UO2 alteration in water

Cited by 150 publications

References 28 publications

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Energetics of metastudtite and implications for nuclear waste alteration

The U₂₈ Nanosphere: What's Inside?

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Alpha-radiolysis effects on UO2 alteration in water

Cited by 150 publications

References 28 publications

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Energetics of metastudtite and implications for nuclear waste alteration

The U28 Nanosphere: What's Inside?

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The U₂₈ Nanosphere: What's Inside?