TY - JOUR
T1 - Radiation-induced decomposition of U(VI) phases to nanocrystals of UO2
AU - Utsunomiya, Satoshi
AU - Ewing, Rodney C.
AU - Wang, Lu Min
N1 - Funding Information:
The authors thank the staff of the IVEM-Tandem Facility at Argonne National Laboratory for assistance during the ion irradiation experiments. S.U. thanks J. F. Mansfield and C. J. Wouchope of the Electron Microbeam Analysis Laboratory at University of Michigan. This work was initiated with support by US DOE, Office of Basic Energy Sciences under grant DE-FGO7-97ER14816, with continuing support from Office of Science and Technology and International (OSTI) of the Office of Civilian Radioactive Waste Management (DE-FE28-04RW12254). The views, opinions, findings, and conclusions or recommendations of the authors expressed herein do not necessarily state or reflect those of the DOE/OCRWM/OSTI.
PY - 2005/12/1
Y1 - 2005/12/1
N2 - 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.
AB - 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.
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U2 - 10.1016/j.epsl.2005.09.034
DO - 10.1016/j.epsl.2005.09.034
M3 - Article
AN - SCOPUS:28044440289
SN - 0012-821X
VL - 240
SP - 521
EP - 528
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 2
ER -