Long-term kinetic effects and colloid formations in dissolution of LWR spent fuels

Ahn, T.

doi:10.2172/414311

Cited by 4 publications

(3 citation statements)

References 61 publications

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“…1, middle) and detachment of waste-form particles from the solid surface or surface alteration layers are further possible colloid-generating mechanisms. Colloid formation upon nuclear waste form contacted with groundwater has been observed in various studies (summarized in Ahn 1996;Geckeis et al 1998). Colloidal Np, Pu, and U species have been found to Fig.…”

Section: Colloid Generation Processes and Colloid Stabilitymentioning

confidence: 87%

Colloid influence on the radionuclide migration from a nuclear waste repository

Geckeis¹

2004

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Colloid formation is discussed as a possible pathway for the radionuclide release from a nuclear waste repository. An assessment of the colloid relevance on radionuclide migration requires insight into the possible colloid generation mechanisms, their stability and mobility under given groundwater conditions. In various experiments dedicated to the investigation of nuclear waste form behaviour in contact with groundwater, colloidal species are observed mainly for the tri-and tetravalent actinides even in rather high ionic strength solutions where destabilization of colloids is expected. Experimental evidence of laboratory and field studies suggests colloid instability in saline groundwater with time. Groundwater of low ionic strength and high pH enhances colloid stability, as demonstrated in various laboratory and field experiments. The results of an in situ colloid characterization study at the Asp6 hard rock laboratory in Sweden are discussed as an example. The mechanism of radionuclide interaction with colloids and notably the reversibility of the radionuclide-colloid binding are other key issues of colloid studies. Kinetic stabilization of the radionuclide binding to colloids may lead to a considerable enhancement of the colloid-mediated radionuclide migration. Substantial kinetic inhibition of actinide dissociation from humic colloids has been established by studying the behaviour of natural humic colloid borne U, Th and rare earth elements. Such behaviour might be explained by the incorporation of these elements into inorganic nanoparticles stabilized by humic coating. Spectroscopic evidence for the occurrence of actinide incorporation into colloidal structures is briefly discussed and the importance of considering the kinetics involved in all kinds of colloidal processes is emphasized. The enhanced migration of tri-and tetravalent actinide ions has been observed recently in various in situ dipole tests at the Grimsel hard rock laboratory in Switzerland. Such experimental findings underline the necessity of further studies on the colloid influence on actinide mobility. Moreover, an improved understanding of colloid-rock interaction mechanisms is required, which is essential for the description and prediction of colloid filtration processes.The reliable long-term safety assessment of a nuclear waste repository requires the quantification of all processes that may affect the isolation of the nuclear waste from the biosphere. The colloid-mediated radionuclide migration is discussed as a possible pathway for radionuclide release. As soon as groundwater has access to the nuclear waste, a complicated interactive network of physical and chemical reactions is initiated, and may lead to: (1) radionuclide mobilization; (2) radionuclide retardation by surface sorption and co-precipitation reactions; and (3) radionuclide immobilization by mineralization reactions, that is, the inclusion of radionuclides into thermodynamically or kinetically stabilized solid host matrices.Ninety years ago, Paneth observed for the first ...

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Section: Colloid Generation Processes and Colloid Stabilitymentioning

confidence: 87%

Colloid influence on the radionuclide migration from a nuclear waste repository

Geckeis¹

2004

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“…This research program will provide a basis for establishing the extent to which models of alteration and corrosion processes used in the performance assessment of the near-field repository environment are useful or valid. For example, it is essential that the presently large uncertainties inherent in these models be reduced (see for example the discussion by Ahn, 1996aAhn, , 1996b. Studies of natural samples of great age and appropriate geochemical environments offer a means to improve the understanding of the sources of error while decreasing uncertainties in the corrosion models.…”

Section: Significance Of Research Program To the Emspmentioning

confidence: 99%

Corrosion of Spent Nuclear Fuel: The Long-Term Assessment

Ewing¹

2004

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Spent nuclear fuel (SNF), essentially UO 2 , accounts for over 95% of the total radioactivity of all of the radioactive wastes in the United States that require disposal, disposition or remediation. The UO 2 in SNF is not stable under oxidizing conditions and may also be altered under reducing conditions. The alteration of SNF results in the formation of new uranium phases that can cause the release or retardation of actinide and fission product radionuclides. Over the long term, and depending on the extent to which the secondary uranium phases incorporate fission products and actinides, these alteration phases become the near-field source term.This research program has been a broadly based effort to understand the long-term behavior of SNF and its alteration products in a geologic repository. 4. Are the corrosion products accurately predicted from geochemical codes (e.g., EQ3/6 or Geochemist's Workbench) that are used in performance assessments? Can these codes be tested by studies of natural analogue sites (e.g., Oklo, Cigar Lake or Pena Blanca).As detailed in the summary of results, we have made substantial progress in addressing each of the above issues.4

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“…In reality, though, preoxidation increases concentrations of dissolved actinides more than SF without preoxidation at 25 and 85 C in 5-13 well water, by at least a factor of 10 (Wilson, 1990). Low-solubility radionuclides are also known to form colloids, under static conditions (Ahn, 1995;Wilson, 1990) or under dripping groundwater conditions (Ahn, 1995;Finn et al, 1994;Wronkiewicz et al, 1992). Up to now, colloid formation has been reported only under oxidizing conditions.…”

Section: Fracture Pathmentioning

confidence: 99%

Dry oxidation and fracture of LWR spent fuels

Ahn¹

1996

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Long-term kinetic effects and colloid formations in dissolution of LWR spent fuels

Cited by 4 publications

References 61 publications

Colloid influence on the radionuclide migration from a nuclear waste repository

Colloid influence on the radionuclide migration from a nuclear waste repository

Corrosion of Spent Nuclear Fuel: The Long-Term Assessment

Dry oxidation and fracture of LWR spent fuels

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