Paper AS-ThP1
Applications of EMSL’s Radiochemistry Annex (RadEMSL) in Understanding of the Chemical Fate and Transport of Radionuclides in Terrestrial and Subsurface Ecosystems

Thursday, October 22, 2015, 6:00 pm, Room Hall 3

(RadEMSL) is a radiochemistry facility, which is part of EMSL, Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at PNNL. This facility is designed to accelerate scientific discovery and deepen the understanding of the chemical fate and transport of radionuclides in terrestrial and subsurface ecosystems. In this poster we present results obtained from two different studies that have utilized the X-ray Photoelectron Spectroscopy (XPS) capability in this facility.

The first application involved XPS analysis of Uraninite (UO₂). UO₂ is the primary component of most nuclear fuels, and can be a major phase in bio-remediated uranium- contaminated soils and aquifers. Understanding the mechanisms of UO₂ surface oxidation and corrosion is essential to predicting its stability in the environment throughout the nuclear fuel cycle. XPS shows clear evidence of U(IV) and U(V) oxidation states consistent with computational results. This new mechanism may be relevant to other fluorite structures, including plutonium dioxide (PuO₂).

The second application involves XPS analysis of Np. Neptunium (Np) is a long-lived radionuclide environmental contaminant associated with weapons production and processing that is transported in the subsurface as actinyl NpO₂⁺. The radioactive metallic element Np is created when uranium-based nuclear fuel is burned up in electricity-producing commercial reactors and in plutonium-producing reactors operated for military purposes. Researchers examined factors that impact structural incorporation of Np(V) neptunyl and U(VI) uranyl ions into carbonate and sulfate minerals. Co-precipitation of Np(V) into mineral structures could reduce transport in the subsurface and shows promise as a groundwater remediation strategy.

Rad(EMSL) offers experimental and computational tools uniquely suited for actinide chemistry studies. The spectroscopic and imaging instruments at this facility are ideally designed for the study of contaminated environmental materials, examination of radionuclide speciation and detection of chemical signatures. The annex houses nuclear magnetic resonance instruments and surface science capabilities, such as X-ray photoelectron spectroscopy, electron microscopy, electron microprobe, transmission electron microscopy and scanning electron microscopy.