Evidence for Neptunium Incorporation into Uranium (VI) Phases

Conference · Wed Dec 01 04:00:00 EST 2004

OSTI ID:15011281

Buck, Edgar C; Hanson, Brady D; Friese, Judah I; Douglas, Matthew; McNamara, Bruce K

This paper examines the ability of Electron Energy-Loss Spectroscopy (EELS) on the Transmission Electron Microscope (TEM) to both detect low levels of neptunium (Np) in a uranium matrix and to provide evidence for incorporation of Np in U6+ phases. The case for using U6+ secondary minerals as solubility-controlling phases for Np in repository performance assessment models has not been established. Direct evidence for incorporation rather than sorption has been difficult to obtain. The detection of Np in a matrix of uranium (U) can be impeded by the occurrence of a plural scattering event from U (U-M5 + U-O4,5) that results in severe overlap on the Np-M5 edge at 3665 eV. By examining the energy gap between the Np-M5 and Np-M4 edges (184 eV), a method for observing Np independently of the plural scattering event has been established. Clear evidence of Np incorporation into studtite, [(UO2)(O2)(H2O)2](H2O)2 and uranophane, Ca(UO2)2(SiO3OH)2(H2O)5 has been found in laboratory tests using TEM-EELS. This data suggests that U6+ phases, if present, may control Np solubility in a repository environment.

• Research Organization: Pacific Northwest National Lab., Richland, WA (US), Environmental Molecular Sciences Laboratory (US)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15011281
• Report Number(s): PNNL-SA-41685; 2472; 830403000
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
DETECTION
EELS
ELECTRON MICROSCOPES
ELECTRONS
ENERGY GAP
ENERGY-LOSS SPECTROSCOPY
ENVIRONMENTAL MOLECULAR SCIENCES LABORATORY
MANAGEMENT
NEPTUNIUM
PERFORMANCE
RADIOACTIVE WASTES
SCATTERING
SOLUBILITY
SORPTION
SPENT FUEL
URANIUM
URANOPHANE
YUCCA MOUNTAIN