Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion

Neill, Thomas S.; Morris, Katherine; Pearce, Carolyn I.; Abrahamsen-Mills, Liam; Kovařík, Libor; Kellet, Simon; Rigby, Bruce; Vitova, T.; Schacherl, Bianca; Shaw, Samuel

doi:10.1016/j.jnucmat.2019.151751

Cited by 10 publications

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“…While UO 2 did not form colloids in this study, previous work has shown that UO 2 can form colloids in the presence of silicates. 9 , 11 Given that U(IV)–silicate colloids can form at alkaline pH, it is important to understand the impact of both UO 2 and U(IV)–silicates on Sr behavior in order to predict Sr mobility where Sr and U are both present. Additionally, the surface incorporation in UO 2 could result in less labile Sr at neutral/alkaline pH as desorption was only observed at acidic pH (<3.2).…”

Section: Discussionmentioning

confidence: 99%

“…Under these conditions, the corrosion of metallic U produces UO 2 , 8 − 11 which has been observed during CMS characterization and metallic U corrosion experiments. 8 , 9 Many other forms of nuclear fuel use UO 2 as a fuel matrix, 2 making UO 2 abundant in most SNF storage scenarios. Importantly, under groundwater conditions (pH 8.4, 41 ppm Si), corrosion of metallic U in SNF can lead to the formation of U(IV) colloids.…”

Section: Introductionmentioning

confidence: 99%

“… 13 , 14 Furthermore, recent work indicates that UO 2 colloidal particles in many storage and disposal environments may have a silicate coating. 9 The mobility of these relatively newly identified U(IV)–silicate colloidal phases is predicted to be high. In turn, this could impact the mobility of associated radionuclides, including 90 Sr, during effluent treatment of waste streams originating from SNF storage facilities.…”

Section: Introductionmentioning

confidence: 99%

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Sorption of Strontium to Uraninite and Uranium(IV)–Silicate Nanoparticles

et al. 2022

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Spent nuclear fuel contains both uranium (U) and high yield fission products, including strontium-90 ( 90 Sr), a key radioactive contaminant at nuclear facilities. Both U and 90 Sr will be present where spent nuclear fuel has been processed, including in storage ponds and tanks. However, the interactions between Sr and U phases under ambient conditions are not well understood. Over a pH range of 4–14, we investigate Sr sorption behavior in contact with two nuclear fuel cycle relevant U(IV) phases: nano-uraninite (UO 2 ) and U(IV)–silicate nanoparticles. Nano-UO 2 is a product of the anaerobic corrosion of metallic uranium fuel, and UO 2 is also the predominant form of U in ceramic fuels. U(IV)–silicates form stable colloids under the neutral to alkaline pH conditions highly relevant to nuclear fuel storage ponds and geodisposal scenarios. In sorption experiments, Sr had the highest affinity for UO 2 , although significant Sr sorption also occurred to U(IV)–silicate phases at pH ≥ 6. Extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy, and desorption data for the UO 2 system suggested that Sr interacted with UO 2 via a near surface, highly coordinated complex at pH ≥ 10. EXAFS measurements for the U(IV)–silicate samples showed outer-sphere Sr sorption dominated at acidic and near-neutral pH with intrinsic Sr-silicates forming at pH ≥ 12. These complex interactions of Sr with important U(IV) phases highlight a largely unrecognized control on 90 Sr mobility in environments of relevance to spent nuclear fuel management and storage.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sorption of Strontium to Uraninite and Uranium(IV)–Silicate Nanoparticles

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“…The samples were removed from the pH 9 0 wt % U(VI) and the pH 7 1 wt % U(VI) colloidal suspensions (at 24 h and 2 cm below the meniscus), pipetted onto carbon-coated gold TEM grids (Agar Scientific), and gently washed with ethanol (2 × 0.5 mL) and deionized water (2 × 0.5 mL) prior to analysis. 54 To obtain the colloidal particle size distributions, bright-field TEM images were taken from the samples using a FEI TF30 TEM. To understand the U(VI) adsorption sites, high-angle annular dark-field (HAADF) STEM images were taken using a FEI Titan G2 S/TEM.…”

Section: Experimental Sectionmentioning

confidence: 99%

Hydrotalcite Colloidal Stability and Interactions with Uranium(VI) at Neutral to Alkaline pH

et al. 2022

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In the United Kingdom, decommissioning of legacy spent fuel storage facilities involves the retrieval of radioactive sludges that have formed as a result of corrosion of Magnox nuclear fuel. Retrieval of sludges may re-suspend a colloidal fraction of the sludge, thereby potentially enhancing the mobility of radionuclides including uranium. The colloidal properties of the layered double hydroxide (LDH) phase hydrotalcite, a key product of Magnox fuel corrosion, and its interactions with U(VI) are of interest. This is because colloidal hydrotalcite is a potential transport vector for U(VI) under the neutral-to-alkaline conditions characteristic of the legacy storage facilities and other nuclear decommissioning scenarios. Here, a multi-technique approach was used to investigate the colloidal stability of hydrotalcite and the U(VI) sorption mechanism(s) across pH 7–11.5 and with variable U(VI) surface loadings (0.01–1 wt %). Overall, hydrotalcite was found to form stable colloidal suspensions between pH 7 and 11.5, with some evidence for Mg 2+ leaching from hydrotalcite colloids at pH ≤ 9. For systems with U present, >98% of U(VI) was removed from the solution in the presence of hydrotalcite, regardless of pH and U loading, although the sorption mode was affected by both pH and U concentrations. Under alkaline conditions, U(VI) surface precipitates formed on the colloidal hydrotalcite nanoparticle surface. Under more circumneutral conditions, Mg 2+ leaching from hydrotalcite and more facile exchange of interlayer carbonate with the surrounding solution led to the formation of uranyl carbonate species (e.g., Mg(UO 2 (CO 3 ) 3 ) 2– (aq) ). Both X-ray absorption spectroscopy (XAS) and luminescence analysis confirmed that these negatively charged species sorbed as both outer- and inner-sphere tertiary complexes on the hydrotalcite surface. These results demonstrate that hydrotalcite can form pseudo-colloids with U(VI) under a wide range of pH conditions and have clear implications for understanding the uranium behavior in environments where hydrotalcite and other LDHs may be present.

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“…Second, the fact that actinides tend to form colloids of aggregated nanoparticles [8,9]. Indeed, in contact with water, metallic U corrosion is known to form fine UO 2 particulates [10,11].…”

Section: Introductionmentioning

confidence: 99%

Uranium Dioxide Nanoparticulated Materials

Soldati¹,

Lago²,

Prado³

2021

Nuclear Materials

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Nanostructured actinide materials have gained the attention of the nuclear community after the discovery of enhanced properties in fuels that undergo high burn up. On these conditions, the UO 2 grains experimented recrystallization and formed a new rim of UO 2 nanoparticles, called high burn up structures (HBS). The pellets with HBS showed closed porosity with better fission gas retention and radiation tolerance, ameliorated mechanical properties, and less detriment of the thermal conductivity upon use. In this chapter, we will review different ways to obtain uranium nanoparticles, with emphasis on their synthesis and characterization. On the one hand, we will comment on radiation chemical syntheses, organic precursor-assisted syntheses, denitration processes, and biologically mediated syntheses. On the other hand, we will include for each of them a reference to the appropriate tools of the materials science that are used to fully characterize physical and chemical properties of these actinide nanoparticles.

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Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion

Cited by 10 publications

References 40 publications

Sorption of Strontium to Uraninite and Uranium(IV)–Silicate Nanoparticles

Sorption of Strontium to Uraninite and Uranium(IV)–Silicate Nanoparticles

Hydrotalcite Colloidal Stability and Interactions with Uranium(VI) at Neutral to Alkaline pH

Uranium Dioxide Nanoparticulated Materials

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