Neptunium(V) Partitioning to Uranium(VI) Oxide and Peroxide Solids
Metaschoepite, [(UO{sub 2}){sub 8}O{sub 2}(OH){sub 12}]{center_dot}10H{sub 2}O, and metastudtite, UO{sub 4} {center_dot} 4H{sub 2}O, are alteration phases anticipated in a spent nuclear fuel repository following the moist oxidation of UO{sub 2} on a geologic timescale. Dissolved concentrations and hence potential mobility of other radionuclides in the fuel, such as the neptunyl cation (NpO{sub 2}{sup +}), will likely be determined by the extent of their partitioning into these U(VI) solids. {sup 237}Np is of particular interest due to its potential high mobility and long half-life (2.1 x 10{sup 6} years.) In this study, metaschoepite has been precipitated and subsequently transformed to studtite in the presence of dissolved Np. The metaschoepite and studtite solids that formed initially contained <10 ppm and 6,500 ppm Np, respectively. Batch dissolution studies of these solids at pH 6 demonstrate release of Np that exceeds congruent dissolution of U from metastudtite; furthermore, the released Np cation remains in solution. Thus, although the Np partitions into the metastudtite solid initially, it is released to solution over time, indicating that metastudtite is not likely to serve as a host solid for Np incorporation or sorption of the neptunyl cation on long time scales.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15016476
- Report Number(s):
- PNNL-SA-44460; ESTHAG; 830403000; TRN: US0502381
- Journal Information:
- Environmental Science and Technology, Vol. 39, Issue 11; Other Information: PBD: 1 Jun 2005; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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