Radiation-induced decomposition of U(VI) phases to nanocrystals of UO2

Satoshi Utsunomiya, Rodney C. Ewing, Lu Min Wang

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


U6+-phases are common alteration products, under oxidizing conditions, of uraninite and the UO2 in spent nuclear fuel. These U6+-phases are subjected to a radiation field caused by the α-decay of U, or in the case of spent nuclear fuel, incorporated actinides, such as 239Pu and 237Np. In order to evaluate the 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+) of U6+-phases. The heavy-particle irradiations are used to simulate the ballistic interactions of the recoil-nucleus of an α-decay event with the surrounding structure. The Kr2+ -irradiation decomposed the U6+-phases to UO2 nanocrystals at doses as low as 0.006 displacements per atom (dpa). U6+-phases accumulate substantial radiation doses (∼1.0 displacement per atom) within 100,000 yr if the concentration of incorporated 239Pu is as high as 1 wt.%. Similar nanocrystals of UO2 were observed in samples from the natural fission reactors at Oklo, Gabon. Multiple cycles of radiation-induced decomposition to UO2 followed by alteration to U6+-phases provide a mechanism for the remobilization of incorporated radionuclides.

Original languageEnglish
Pages (from-to)521-528
Number of pages8
JournalEarth and Planetary Science Letters
Issue number2
Publication statusPublished - Dec 1 2005
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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