Abstract
| Original language | English |
|---|---|
| Pages (from-to) | 763 - 766 |
| Number of pages | 4 |
| Journal | Radiochimica Acta |
| Volume | 88 |
| Issue number | 9-11 |
| DOIs | |
| Publication status | Published - 2000 |
| MoE publication type | A1 Journal article-refereed |
| Event | 7th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere - Lake Tahoe, United States Duration: 26 Sep 1999 → 1 Oct 1999 |
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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 journal › Article › Scientific › peer-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
VL - 88
SP - 763
EP - 766
JO - Radiochimica Acta
JF - Radiochimica Acta
SN - 0033-8230
IS - 9-11
ER -