TY - JOUR
T1 - Microscale characterization of uranium(VI) silicate solids and associated neptunium(V)
AU - Douglas, Matthew
AU - Clark, Sue B.
AU - Friese, Judah I.
AU - Arey, Bruce W.
AU - Buck, Edgar C.
AU - Hanson, Brady D.
AU - Utsunomiya, Satoshi
AU - Ewing, Rodney C.
N1 - Funding Information:
Acknowledgment. Primary funding for this work was provided by the U.S. Department of Energy’s Office of Science Basic Energy Sciences program under contract DE-FG02-01ER15138. Support from the NSF Integrative Graduate Education and Research Training (IGERT) program in the Center for Multiphase Environmental Research at Washington State University under grant DGE-9972817 and from the Yucca Mountain Project supported by DOE, Office of Civilian Radioactive Waste Management is acknowledged. The TEM work was performed at the EMSL, a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory, operated for DOE by Battelle.
PY - 2005
Y1 - 2005
N2 - The uranium(VI) silicate phases uranophane, Ca[(UO2)(SiO 3OH)]2·5H2O, and sodium boltwoodite, Na[(UO2)(SiO3OH)]-1.5H2O, were synthesized in the presence of small, variable quantities (0.5-2.0 mol % relative to U) of pentavalent neptunium (Np(V), as NpO2+), to investigate the nature of its association with these U(VI) solid phases. Solids were characterized by X-ray powder diffraction (XRD), gamma spectrometry (GS), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) with electron energy-loss spectroscopy (EELS). Neptunium concentration was determined in the bulk solid phases by GS and was found to range from 780-15800μg/g. In some cases, Np distributions between the aqueous and solid phases were monitored, and 78%-97% of the initial Np was associated with the isolated solid. Characterization of individual crystallites by TEM/EELS suggests the Np is associated with the U(VI) phase. No discrete Np phases, such as Np oxides, were observed. Because the U(VI) silicates are believed to be important solubility-controlling solids on a geologic timescale, these results suggest that the partitioning of the minor actinides to these solids must be considered when assessing the performance of a waste repository for spent nuclear fuel.
AB - The uranium(VI) silicate phases uranophane, Ca[(UO2)(SiO 3OH)]2·5H2O, and sodium boltwoodite, Na[(UO2)(SiO3OH)]-1.5H2O, were synthesized in the presence of small, variable quantities (0.5-2.0 mol % relative to U) of pentavalent neptunium (Np(V), as NpO2+), to investigate the nature of its association with these U(VI) solid phases. Solids were characterized by X-ray powder diffraction (XRD), gamma spectrometry (GS), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) with electron energy-loss spectroscopy (EELS). Neptunium concentration was determined in the bulk solid phases by GS and was found to range from 780-15800μg/g. In some cases, Np distributions between the aqueous and solid phases were monitored, and 78%-97% of the initial Np was associated with the isolated solid. Characterization of individual crystallites by TEM/EELS suggests the Np is associated with the U(VI) phase. No discrete Np phases, such as Np oxides, were observed. Because the U(VI) silicates are believed to be important solubility-controlling solids on a geologic timescale, these results suggest that the partitioning of the minor actinides to these solids must be considered when assessing the performance of a waste repository for spent nuclear fuel.
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U2 - 10.1524/ract.93.5.265.64281
DO - 10.1524/ract.93.5.265.64281
M3 - Article
AN - SCOPUS:19144369424
SN - 0033-8230
VL - 93
SP - 265
EP - 272
JO - Radiochimica Acta
JF - Radiochimica Acta
IS - 5
ER -