Corrections to the Uranium NEA-TDB review

Grenthe, Ingmar; Sandino, M. C. A.; Puigdomènech, I.; Rand, M. H.

doi:10.1016/b978-0-444-82281-9.50020-9

Cited by 49 publications

(76 citation statements)

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“…These are derived from experimental measurements of variable quality. Grenthe et al (1992Grenthe et al ( , 1995 and Guillaumont and Mompean (2003) have extensively reviewed the literature database on aqueous-complexation reactions of U(VI) and, from these, suggest the most experimentally robust and statistically defensible values. These accepted and reviewed values have been used for all calculations in this report.…”

Section: Computerized Aqueous Speciation Calculationsmentioning

confidence: 99%

A Site Wide Perspective on Uranium Geochemistry at the Hanford Site

Zachara¹,

Brown²,

Christensen³

et al. 2007

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Executive SummaryUranium (U) is an important risk-driving contaminant at the Hanford Site. Over 200,000 kg have been released to the vadose zone over the course of site operations, and a number of vadose zone and groundwater plumes containing the uranyl cation [UO 2 2+ , U(VI)] have been identified. U is recognized to be of moderate-to-high mobility, conditions dependent. The site is currently making decisions on several of these plumes with long-lasting implications, and others are soon to come.Uranium is one of nature's most intriguing and chemically complex elements. The fate and transport of U(VI) has been studied over the long lifetime of the Hanford Site by various contractors, along with the Pacific Northwest National Laboratory (PNNL) and its collaborators. Significant research has more recently been contributed by the national scientific community with support from the U.S. Department of Energy's (DOE) Office of Science through its Environmental Remediation Sciences Division (ERSD). This report represents a first attempt to integrate these findings into a cohesive view of the subsurface geochemistry of U at the Hanford Site. The objective is to inform all interested Hanford parties about the in-ground inventory of U and its geochemical behavior. This report also comments on the prospects for the development of a robust generic model to more accurately forecast future U(VI) migration at different Hanford waste sites, along with further research necessary to reach this goal.To accomplish the report objectives, the environmental geochemistry of U at the Hanford Site is discussed in terms of both the vadose and saturated zone, to the extent that it is known. Hexavalent uranium [U(VI)] is the dominant valence form of U under the predominantly oxidizing subsurface conditions at the Hanford Site, and the researchers' analyses consequently emphasize this species. The nature and concentration of background U in Hanford subsurface sediments is identified to place contaminant U(VI) concentrations and behavior in perspective to the natural system. In-ground U-waste inventories are quantified and characterized with regard to source term, to the extent possible, and the most important sites from an inventory perspective are identified. The U-isotopic content of various waste streams are discussed from the perspective of waste-source tracking. The geochemical attenuation processes responsible for slowing the rate of subsurface U migration, relative to the transporting water front, are illustrated through careful consideration of both field characterization studies of existing U vadose-zone and groundwater plumes, and laboratory studies of derived contaminated and uncontaminated sediments. Both empirical and more mechanistic models of these attenuation processes are considered as well as the parameters that define attenuation magnitude. Attention is given to the behavior of contaminant U(VI) that has been in contact with Hanford sediments for extended periods (circa 10-50 years), as long contact imparts unique characte...

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Section: Computerized Aqueous Speciation Calculationsmentioning

confidence: 99%

A Site Wide Perspective on Uranium Geochemistry at the Hanford Site

Zachara¹,

Brown²,

Christensen³

et al. 2007

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“…The theoretical predictions were performed by means of the JCHESS software developed by Ecole des Mines de Paris, 16 using the OECD/NEA thermodynamic database, 17 although some interrogations remain on some of the formation constants, especially for the various carbonato species. 18 For the calculations, the values of pCO 2 (3x10 -4 ), together with the dissociation constants of H 2 SO 4 and HF were taken into account.…”

Section: Speciation Calculationsmentioning

confidence: 99%

Aqueous Solutions of Uranium(VI) as Studied by Time-Resolved Emission Spectroscopy: A Round-Robin Test

et al. 2003

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Results are presented of an interlaboratory round-robin study of the application of timeResolved Emission Spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media. This involved 13 independent laboratories, using various instrumental adevices and data 2 analysis methods. In some cases, experimental data from a laboratory were analysed using different softwares. Samples were prepared based on appropriate speciation diagrams and in general were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (i) acidic medium where UO 2 2+ aq is the single emitting species, (ii) uranyl in the presence of fluoride ions, (iii) uranyl in the presence of sulfate ions, and (iv) uranyl in aqueous solutions under various pH conditions, promoting hydrolysed species. Results between the laboratories are compared in terms of number of decay components, luminescence lifetimes and spectral band positions. The potentials and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.

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“…When sodium boltwoodite encounters phosphates and silicates, U(VI) precipitates as sparingly soluble minerals such as metaschoepite (UO3·2H2O) and various phosphates and silicates (Grenthe et al, 1995). In natural environments, diatom frustules and silts were reported to contain higher levels of uranium due to entrapment of small clay particles by their silicaceous tests or by binding with organic matter (Edgington et al, 1996;Gavshin et al, 2001).…”

Section: Uranium Biomineralization With Silicatementioning

confidence: 99%