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Title: The role of surfaces, chemical interfaces, and disorder on plutonium incorporation in pyrochlores

Journal Article · · Physical Chemistry Chemical Physics. PCCP
DOI:https://doi.org/10.1039/C6CP03543D· OSTI ID:1346846

Pyrochlores, a class of complex oxides with formula A2B2O7, are one of the candidates for nuclear waste encapsulation, due to the natural occurrence of actinide-bearing pyrochlore minerals and laboratory observations of high radiation tolerance. In this work, we use atomistic simulations to determine the role of surfaces, chemical interfaces, and cation disorder on the plutonium immobilization properties of pyrochlores as a function of pyrochlore chemistry. We find that both Pu3+ and Pu4+ segregate to the surface for the four low-index pyrochlore surfaces considered, and that the segregation energy varies with the chemistry of the compound. We also find that pyrochlore/pyrochlore bicrystals A2B2O7/A2'B2'O7 can be used to immobilize Pu3+ and Pu4+ either in the same or separate phases of the compound, depending on the chemistry of the material. Finally, we find that Pu4+ segregates to the disordered phase of an order/disorder bicrystal, driven by the occurrence of local oxygen-rich environments. However, Pu3+ is weakly sensitive to the oxygen environment, and therefore only slightly favors the disordered phase. This behavior suggests that, at some concentration, Pu incorporation can destabilize the pyrochlore structure. Together, these results provide new insight into the ability of pyrochlore compounds to encapsulate Pu and suggest new considerations in the development of waste forms based on pyrochlores. Particularly, the phase structure of a multi-phase pyrochlore composite can be used to independently getter decay products based on their valence and size.

Research Organization:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC52-06NA25396
OSTI ID:
1346846
Report Number(s):
LA-UR-16-26968; PPCPFQ; TRN: US1701759
Journal Information:
Physical Chemistry Chemical Physics. PCCP, Vol. 18, Issue 33; ISSN 1463-9076
Publisher:
Royal Society of ChemistryCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 19 works
Citation information provided by
Web of Science

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  • Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Vol. 268, Issue 19 https://doi.org/10.1016/j.nimb.2010.05.030
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