Corrosion of commercial spent nuclear fuel. 1. Formation of studtite and metastudtite

Hanson, Brady D.; McNamara, Bruce K.; Buck, Edgar C.; Friese, Judah I.; Jenson, Evan D.; Krupka, Kenneth M.; Arey, Bruce W.

doi:10.1524/ract.93.3.159.61613

Cited by 101 publications

(91 citation statements)

References 20 publications

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“…Previous studies (3,5,14) on studtite found its stability was strongly improved when H 2 O 2 , generated and replenished by radiolysis of water, is present (14). With the presence of H 2 O 2 , this locally oxidizing condition is also expected to stabilize the metastudtite phase.…”

Section: Discussionmentioning

confidence: 96%

“…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. Also UO 3 ·xH 2 O (x < 2), metaschoepite, was found to form as an oxidation product on the surface of UO 2 samples.…”

mentioning

confidence: 84%

“…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%

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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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Section: Discussionmentioning

confidence: 96%

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confidence: 84%

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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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“…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).…”

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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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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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“…25,26 But the acicular morphology is also consistent with studtite particles previously observed using SEM. 27,28 As SEM observation is not capable of differentiating between the two uranyl minerals, we tried transmission electron microscopy (TEM). However, all U-rich particles analyzed using selected area electron diffraction (SAED) show a very fast structural transformation under the TEM beam, which consists of the amorphization of the original crystalline particles followed by the formation of nanouraninite ( Figure S5).…”

Section: Environmental Science and Technologymentioning

confidence: 99%

Products of in Situ Corrosion of Depleted Uranium Ammunition in Bosnia and Herzegovina Soils

Wang

Gunten

Bártová

et al. 2016

Environ. Sci. Technol.

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Hundreds of tons of depleted uranium (DU) ammunition were used in previous armed conflicts in Iraq, Bosnia and Herzegovina, and Serbia/Kosovo. The majority (>90%) of DU penetrators miss their target and, if left in the environment, corrode in these postconflict zones. Thus, the best way to understand the fate of bulk DU material in the environment is to characterize the corrosion products of intact DU penetrators under field conditions for extended periods of time. However, such studies are scarce. To fill this knowledge gap, we characterized corrosion products formed from two intact DU penetrators that remained in soils in Bosnia and Herzegovina for over seven years. We used a combination of X-ray powder diffraction, electron microscopy, and X-ray absorption spectroscopy. The results show that metaschoepite (UO 3 (H 2 O) 2 ) was a main component of the two DU corrosion products. Moreover, studtite ((UO 2 )O 2 (H 2 O) 2 ·2(H 2 O)) and becquerelite (Ca(UO 2 ) 6 O 4 (OH) 6 ·8(H 2 O)) were also identified in the corrosion products. Their formation through transformation of metaschoepite was a result of the geochemical conditions under which the penetrators corroded. Moreover, we propose that the transformation of metaschoepite to becquerelite or studtite in the DU corrosion products would decrease the potential for mobilization of U from corroded DU penetrators exposed to similar environments in postconflict areas.

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Corrosion of commercial spent nuclear fuel. 1. Formation of studtite and metastudtite

Abstract: SummaryThe contact of commercial spent nuclear fuel (CSNF) with water over a 2-year period led to an unexpected corrosion phase and morphology. At short hydration times, crystallites of metaschoepite [(UO

Cited by 101 publications

References 20 publications

Energetics of metastudtite and implications for nuclear waste alteration

Energetics of metastudtite and implications for nuclear waste alteration

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Products of in Situ Corrosion of Depleted Uranium Ammunition in Bosnia and Herzegovina Soils

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