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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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0003-004X
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Volume 94, Issue 2-3

Issues

Stability of uranium (VI) peroxide hydrates under ionizing radiation

Alexandra Rey
  • Department of Chemical Engineering, Universitat Politecnica de Catalunya (UPC), 08028 Barcelona, Spain
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/ Satoshi Utsunomiya
  • Corresponding author
  • Department of Geological Sciences, University of Michigan, Michigan 48109-1005, U.S.A.
  • Department of Geological Sciences, University of Michigan, Michigan 48109-1005, U.S.A.
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/ Javier Giménez
  • Department of Chemical Engineering, Universitat Politecnica de Catalunya (UPC), 08028 Barcelona, Spain
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/ Ignasi Casas
  • Department of Chemical Engineering, Universitat Politecnica de Catalunya (UPC), 08028 Barcelona, Spain
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/ Joan de Pablo
  • Department of Chemical Engineering, Universitat Politecnica de Catalunya (UPC), 08028 Barcelona, Spain
  • Centre Tecnològic, Manresa (CTM), 08242 Manresa, Barcelona, Spain
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/ Rodney C. Ewing
Published Online: 2015-04-01 | DOI: https://doi.org/10.2138/am.2009.2908

Abstract

The uranyl peroxide, studtite (UO4⋅4H2O, C2/c, Z = 4), is expected to form as a consequence of alpha radiolysis of water in contact with spent nuclear fuel (SNF) in a geologic repository. Investigation of its stability is, therefore, of critical importance because secondary U(VI) phases may incorporate trace amounts of radionuclides and thus retard their mobility away from a repository site. To examine the effect of ionizing radiation on uranyl peroxides, electron-beam irradiation experiments have been conducted on two synthetic uranyl peroxides: studtite and metastudtite (UO4⋅2H2O, Immm, Z = 2). All experiments were done using a transmission electron microscope (TEM) with an acceleration voltage of 200 kV at room temperature. The fluence required to completely amorphize studtite was 0.51-1.54 × 1017 e/cm2, which is equivalent to an absorbed dose of 0.73-1.43 × 107 Gy. Metastudtite becomes amorphous at a higher absorbed dose (1.31 × 107 Gy) than studtite, most likely because it contains fewer water molecules in its structure. These uranyl peroxides partially amorphize at doses that are one-tenth of the dose required for complete amorphization. With continued irradiation, uraninite nanocrystals form that are a few nanometers in diameter, at 4-20 × 1010 Gy. In a geologic repository, for spent nuclear fuel, the estimated absorbed doses due to ionizing radiation may be as high as 108-1011 Gy after 106 years. This is well in excess of doses in the laboratory experiments that caused the uranyl peroxides to become amorphous and decompose.

Keywords : Ionizing radiation; TEM; uranyl peroxide; amorphization

About the article

Received: 2007-12-25

Accepted: 2008-09-08

Published Online: 2015-04-01

Published in Print: 2009-02-01


Citation Information: American Mineralogist, Volume 94, Issue 2-3, Pages 229–235, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am.2009.2908.

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© 2015 by Walter de Gruyter Berlin/Boston.Get Permission

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