The U<sub>28</sub> Nanosphere: What's Inside?

Nyman, May; Rodriguez, Mark A.; Alam, Todd M.

doi:10.1002/ejic.201001355

Cited by 53 publications

(101 citation statements)

References 28 publications

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“…Although it is not currently possible to measure the enthalpies of formation of aqueous alkali uranyl peroxide species (22), or complex cage clusters in solution, our studies of the corresponding solid phases provide useful insight pertaining to the interaction of irradiated fuel and seawater. Peroxide production will be the highest where water contacts fuel directly (owing to the importance of alpha radiolysis), and it will achieve the highest concentration locally in the water near the surface of the fuel, where the fuel to water ratio is high, and where water is relatively stagnant.…”

Section: Resultsmentioning

confidence: 99%

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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.

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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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Section: Resultsmentioning

confidence: 99%

“…The synthesis of a mixed Cs∕K or Rb∕K salt similar to KUT was described previously (22). The pure K-salt was synthesized in this study.…”

Section: Methodsmentioning

confidence: 99%

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Armstrong

Nyman

Shvareva

et al. 2012

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

Self Cite

135

177

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“…Initially, aqueous solutions of Li–U 24 , and NH 4 –U 32 were prepared. Comparison of the X‐ray scattering curves to those simulated from the solid‐state structures shows excellent agreement out to three oscillations, indicating absolute monodispersity (Figure ).…”

Section: Resultsmentioning

confidence: 99%

Benchmarking Uranyl Peroxide Capsule Chemistry in Organic Media

et al. 2016

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Uranyl peroxide capsules are a recent addition to polyoxometalate (POM) chemistry. Ten years of development has ensued only in water, while transition metal POMs are commonly exploited in aqueous and organic media, controlled by counterions or ligation to render the clusters hydrophilic or hydrophobic. Here, new uranyl POM behavior is recognized in organic media, including (1) stabilization and immobilization of encapsulated hydrophilic countercations, identified by Li nuclear magnetic resonance (NMR) spectroscopy, (2) formation of new cluster species upon phase transfer, (3) extraction of uranyl clusters from different starting materials including simulated spent nuclear fuel, (4) selective phase transfer of one cluster type from a mixture, and (5) phase transfer of clusters from both acidic and alkaline media. The capsule morphology of the uranyl POMs renders accurate characterization by X‐ray scattering, including the distinction of geometrically similar clusters. Compositional analysis of the aqueous phase post‐extraction provided a quantitative determination of the ion exchange process that enables transfer of the clusters into the organic phase. Preferential partitioning of uranyl POMs into organic media presents new frontiers in metal ion behavior and chemical reactions in the confined space of the cluster capsules in hydrophobic media, as well as the reactivity of clusters at the organic/aqueous interface.

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“…Vibrational spectra are well suited to following inorganic reactions for a variety of reasons: a simple experimental setup, a large pre-existing body of literature on the positions of vibrational bands for a variety of functional groups, [10][11][12][13][14][15][16] and sensitivity to all bonds, regardless of the phase of the material. Furthermore, the large number of synthetic uranyl peroxide cage clusters [17][18][19][20][21][22][23][24][25][26] and extended solids [27][28][29][30][31][32][33][34][35] containing uranium enable us to build an extensive library of correlations between crystallographically determined bond lengths and angles and the positions of Raman bands corresponding to vibrational modes of those bonds. In addition, the experimental configuration allows for spectroscopic observation of any species irradiated by the laser, so that solution and solid-phase species may be observed simultaneously.…”

Section: Introductionmentioning

confidence: 99%

In-Situ Raman Spectroscopy Studies of Room-Temperature and Hydrothermal Reactions

et al. 2012

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By contracting with the Parr Instrument Company and Bruker Optical Systems, we have developed a system for continuous monitoring of hydrothermal and room temperature reactions by Raman spectroscopy. Using the uranyl peroxide cage cluster {[UO 2 (O 2 )(OH)] 16 [UO 2 (O 2 ) 2 ] 4 } 24-(denoted {U 20R }) and a coordination polymer made from uranyl ions and 4,4'-biphenyldicarboxylate as model systems, we demonstrate the spectroscopically observable changes associated with reaction progress and crystallization.

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The U₂₈ Nanosphere: What's Inside?

Cited by 53 publications

References 28 publications

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Benchmarking Uranyl Peroxide Capsule Chemistry in Organic Media

In-Situ Raman Spectroscopy Studies of Room-Temperature and Hydrothermal Reactions

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The U28 Nanosphere: What's Inside?

Cited by 53 publications

References 28 publications

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Uranyl peroxide enhanced nuclear fuel corrosion in seawater

Benchmarking Uranyl Peroxide Capsule Chemistry in Organic Media

In-Situ Raman Spectroscopy Studies of Room-Temperature and Hydrothermal Reactions

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The U₂₈ Nanosphere: What's Inside?