Microscale Characterization of Uranium(VI) Silicate Solids and Associated Neptunium(V)

Journal Article · Wed Jun 01 04:00:00 EDT 2005 · Radiochimica Acta, 93(5):265-272

DOI:https://doi.org/10.1524/ract.93.5.265.64281· OSTI ID:15020637

Douglas, Matt; Clark, Sue B; Friese, Judah I; Arey, Bruce W; Buck, Edgar C; Hanson, Brady D; Utsunomiya, Satoshi; Ewing, Rodney C

The uranium(VI) silicate phases uranophane, Ca[(UO2)(SiO3OH)]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 – 15,800 μg/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.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15020637
• Report Number(s): PNNL-SA-44461; 830403000
• Journal Information: Radiochimica Acta, 93(5):265-272, Journal Name: Radiochimica Acta, 93(5):265-272 Journal Issue: 5 Vol. 93
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
ACTINIDES
DIFFRACTION
ELECTRONS
ENERGY-LOSS SPECTROSCOPY
GAMMA SPECTROSCOPY
NEPTUNIUM
NUCLEAR FUELS
SCANNING ELECTRON MICROSCOPY
SILICATE MINERALS
SILICATES
SODIUM
TRANSMISSION ELECTRON MICROSCOPY
URANIUM MINERALS
URANOPHANE
WASTES
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY
solid solution
spent nuclear fuel
uranium minerals
uranophane
uranyl