Stability of uranium (VI) peroxide hydrates under ionizing radiation

Alexandra Rey, Satoshi Utsunomiya, Javier Giménez, Ignasi Casas, Joan De Pablo, Rodney C. Ewing

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

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 (UO 4·2H2O, 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 × 10 7 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.

Original languageEnglish
Pages (from-to)229-235
Number of pages7
JournalAmerican Mineralogist
Volume94
Issue number2-3
DOIs
Publication statusPublished - 2009

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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