Contrary effects of the water radiolysis product H<sub>2</sub>O<sub>2</sub>upon th dissolution of nuclear fuel in natural ground water and deionized water

Amme, M.

doi:10.1524/ract.2002.90.7_2002.399

Cited by 58 publications

(70 citation statements)

References 17 publications

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“…Initially metaschoepite was formed, but was then replaced by studtite over a 2-year period. When investigating the surface evolution of UO 2 , Hanson et al [11] found that metaschoepite (UO 3 x 1-2H 2 O) is formed upon oxidation by O 2 , whereas leaching in H 2 O 2 leads to the formation of studtite (UO 4 x 4H 2 O), when the H 2 O 2 concentration is sufficiently high [11,12].…”

Section: Introductionmentioning

confidence: 99%

Oxidation of UO2(s) in aqueous solution

Roth

Jönsson

2008

Open Chemistry

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Abstract:In this review the kinetics and mechanism of oxidative dissolution of UO 2 (s), mainly under conditions of relevance for the safety assessment of a deep geological repository for spent nuclear fuel, are discussed. Rate constants for the elementary processes involved (oxidation of UO 2 and dissolution of oxidized UO 2 ) are used to calculate the rates of oxidative UO 2 (s) dissolution under various conditions (type of oxidant, oxidant concentration and HCO 3 -/CO 3 2-concentration) for which experimental data are also available. The calculated rates are compared to the corresponding experimental values under the assumption that the experimental numbers reflect the steady-state conditions of the system. The agreement between the calculated rates and the corresponding experimental ones is very good, in particular for the higher rates. In general, the calculated rates are somewhat higher than the experimental numbers. This can be due partly to the use of initial concentrations rather than steady-state concentrations in the calculations. The kinetic data are also used to quantitatively discuss the dynamics of spent nuclear fuel dissolution under deep geological repository conditions. © Versita Warsaw and Springer-Verlag Berlin Heidelberg.

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Section: Introductionmentioning

confidence: 99%

Oxidation of UO2(s) in aqueous solution

Roth

Jönsson

2008

Open Chemistry

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“…, and studtite, (UO 2 )O 2 (H 2 O) 4 , are the two only known minerals containing peroxide. Metastudtite is the main natural peroxide mineral (1) due to the irreversible dehydration of studtite (2).…”

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confidence: 99%

“…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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“…In this work, we propose to investigate the effect of molecular species produced by 4 proposed a reduction mechanism based on radical interactions with the oxidized U(VI) released into solution.…”

Section: Introductionmentioning

confidence: 99%