Fracture smectite as a long-term sink for natural radionuclides: Indications from unusual U-series disequilibria

H. Marcos (Corresponding Author), J. Suksi, H. Ervanne, Kari Rasilainen

    Research output: Contribution to journalArticleScientificpeer-review

    6 Citations (Scopus)

    Abstract

    Occurrence of natural U in fracture smectite (main mineral component of bentonite) was studied as an analogue to radionuclide behaviour in the near-field of spent nuclear fuel repository. Elevated U content (57 ppm) was observed in fracture smectite sampled from the surface of water-carrying fracture in granite pegmatite at a depth of 70 m. The current groundwater conditions are oxidising at the sampled point. The U-234/U-238 activity ratio (AR) measured in the bulk U and in its sequentially extracted phases, displays unusually low value (around 0.30). Low AR indicates preferential loss of the U-234 isotope from the system. Because the U-234 loss can also be seen in the Th-230/U-234 activity ratio (clearly over 1), the selective removal of the U-234 isotope must have taken place more recently than what is needed to equilibrate Th-230/U-234 pair (i.e. 350000 a). To explain the selective U-234 loss from the smectite we postulate that bulk U is in reduced +4 form and a considerable part of the U-234 isotope in easily leachable oxidised +6 form. This study suggests that the long-term chemical stability of the bulk U in the smectite is due to irreversible fixation of U in the reduced +4 form.
    Original languageEnglish
    Pages (from-to)763 - 766
    Number of pages4
    JournalRadiochimica Acta
    Volume88
    Issue number9-11
    DOIs
    Publication statusPublished - 2000
    MoE publication typeA1 Journal article-refereed
    Event7th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere - Lake Tahoe, United States
    Duration: 26 Sep 19991 Oct 1999

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    montmorillonite
    sinks
    Radioisotopes
    radioactive isotopes
    indication
    Isotopes
    isotopes
    Bentonite
    spent fuels
    bentonite
    nuclear fuels
    Spent fuels
    Chemical stability
    Nuclear fuels
    granite
    axioms
    ground water
    Minerals
    Groundwater
    near fields

    Cite this

    @article{ec383047ee4447968bc9f26ccc3094ec,
    title = "Fracture smectite as a long-term sink for natural radionuclides: Indications from unusual U-series disequilibria",
    abstract = "Occurrence of natural U in fracture smectite (main mineral component of bentonite) was studied as an analogue to radionuclide behaviour in the near-field of spent nuclear fuel repository. Elevated U content (57 ppm) was observed in fracture smectite sampled from the surface of water-carrying fracture in granite pegmatite at a depth of 70 m. The current groundwater conditions are oxidising at the sampled point. The U-234/U-238 activity ratio (AR) measured in the bulk U and in its sequentially extracted phases, displays unusually low value (around 0.30). Low AR indicates preferential loss of the U-234 isotope from the system. Because the U-234 loss can also be seen in the Th-230/U-234 activity ratio (clearly over 1), the selective removal of the U-234 isotope must have taken place more recently than what is needed to equilibrate Th-230/U-234 pair (i.e. 350000 a). To explain the selective U-234 loss from the smectite we postulate that bulk U is in reduced +4 form and a considerable part of the U-234 isotope in easily leachable oxidised +6 form. This study suggests that the long-term chemical stability of the bulk U in the smectite is due to irreversible fixation of U in the reduced +4 form.",
    author = "H. Marcos and J. Suksi and H. Ervanne and Kari Rasilainen",
    year = "2000",
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    language = "English",
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    pages = "763 -- 766",
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    Fracture smectite as a long-term sink for natural radionuclides : Indications from unusual U-series disequilibria. / Marcos, H. (Corresponding Author); Suksi, J.; Ervanne, H.; Rasilainen, Kari.

    In: Radiochimica Acta, Vol. 88, No. 9-11, 2000, p. 763 - 766.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

    T1 - Fracture smectite as a long-term sink for natural radionuclides

    T2 - Indications from unusual U-series disequilibria

    AU - Marcos, H.

    AU - Suksi, J.

    AU - Ervanne, H.

    AU - Rasilainen, Kari

    PY - 2000

    Y1 - 2000

    N2 - Occurrence of natural U in fracture smectite (main mineral component of bentonite) was studied as an analogue to radionuclide behaviour in the near-field of spent nuclear fuel repository. Elevated U content (57 ppm) was observed in fracture smectite sampled from the surface of water-carrying fracture in granite pegmatite at a depth of 70 m. The current groundwater conditions are oxidising at the sampled point. The U-234/U-238 activity ratio (AR) measured in the bulk U and in its sequentially extracted phases, displays unusually low value (around 0.30). Low AR indicates preferential loss of the U-234 isotope from the system. Because the U-234 loss can also be seen in the Th-230/U-234 activity ratio (clearly over 1), the selective removal of the U-234 isotope must have taken place more recently than what is needed to equilibrate Th-230/U-234 pair (i.e. 350000 a). To explain the selective U-234 loss from the smectite we postulate that bulk U is in reduced +4 form and a considerable part of the U-234 isotope in easily leachable oxidised +6 form. This study suggests that the long-term chemical stability of the bulk U in the smectite is due to irreversible fixation of U in the reduced +4 form.

    AB - Occurrence of natural U in fracture smectite (main mineral component of bentonite) was studied as an analogue to radionuclide behaviour in the near-field of spent nuclear fuel repository. Elevated U content (57 ppm) was observed in fracture smectite sampled from the surface of water-carrying fracture in granite pegmatite at a depth of 70 m. The current groundwater conditions are oxidising at the sampled point. The U-234/U-238 activity ratio (AR) measured in the bulk U and in its sequentially extracted phases, displays unusually low value (around 0.30). Low AR indicates preferential loss of the U-234 isotope from the system. Because the U-234 loss can also be seen in the Th-230/U-234 activity ratio (clearly over 1), the selective removal of the U-234 isotope must have taken place more recently than what is needed to equilibrate Th-230/U-234 pair (i.e. 350000 a). To explain the selective U-234 loss from the smectite we postulate that bulk U is in reduced +4 form and a considerable part of the U-234 isotope in easily leachable oxidised +6 form. This study suggests that the long-term chemical stability of the bulk U in the smectite is due to irreversible fixation of U in the reduced +4 form.

    U2 - 10.1524/ract.2000.88.9-11.763

    DO - 10.1524/ract.2000.88.9-11.763

    M3 - Article

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    SP - 763

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    JO - Radiochimica Acta

    JF - Radiochimica Acta

    SN - 0033-8230

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    ER -