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Radiation-induced decomposition of U(VI) alteration phases of UO2

Published online by Cambridge University Press:  21 March 2011

Satoshi Utsunomiya  and
Rodney C. Ewing
Satoshi Utsunomiya
Affiliation:
Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1063, USA
Rodney C. Ewing
Affiliation:
Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1063, USA
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Abstract

U6+−phases are common alteration products of spent nuclear fuel under oxidizing conditions, and they may potentially incorporate actinides, such as long-lived 239Pu and 237Np, delaying their transport to the biosphere. In order to evaluate the ballistic effects of α-decay events on the stability of the U6+−phases, we report, for the first time, the results of ion beam irradiations (1.0 MeV Kr2+) for six different structures of U6+-phases: uranophane, kasolite, boltwoodite, saleeite, carnotite, and liebigite. The target uranyl-minerals were characterized by powder X-ray diffraction and identification confirmed by SAED (selected area electron diffraction) in TEM (transmission electron microscopy). The TEM observation revealed no initial contamination of uraninite in these U6+ phases. All of the samples were irradiated with in situ TEM observation using 1.0 MeV Kr2+ in the IVEM (intermediate-voltage electron microscope) at the IVEM-Tandem Facility of Argonne National Laboratory. The ion flux was 6.3 × 1011 ions/cm2/sec. The specimen temperatures during irradiation were 298 and 673 K, respectively. The Kr2+-irradiation decomposed the U6+-phases to nanocrystals of UO2 at doses as low as 0.006 dpa. The cumulative doses for the pure U6+-phases, e.g., uranophane, at 0.1 and 1 million years (m.y.) are calculated to be 0.009 and 0.09 dpa using SRIM2003. However, with the incorporation of 1 wt.% 239Pu, the calculated doses reach 0.27 and ∼1.00 dpa in ten thousand and one hundred thousand years, respectively.

Under oxidizing conditions, multiple cycles of radiation-induced decomposition to UO2 followed by alteration to U6+-phases should be further investigated to determine the fate of trace elements that may have been incorporated in the U6+-phases.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 932: Symposium – Scientific Basis for Nuclear Waste Management XXIX , 2006 , 73.1
Copyright
Copyright © Materials Research Society 2006

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