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Powell, Brian A.

Publications and source records attributed to Powell, Brian A..

22 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Examination of actinide chemistry at solid-water interfaces to support advanced actinide separations (Final Report)

In this work we have examined the thermodynamics of actinide interactions with solid interfaces in the presence and absence of multi-functional complexing ligands. The term “interactions” is a global term to capture many potential reactions including aqueous complexation, sorption/surface complexation, surface-mediated redox reactions, electrostatic attraction and repulsion, surface passivation, surface precipitation, and counter-ion competition. Each of these potential reactions may control actinide interactions with a solid surface. This work is helping to develop a more fundamental understanding of actinide bonding at solid:water interfaces and examine unique surface mediated oxidation/reduction reactions which are not expected based on the reduction potentials of aqueous species. We place a large emphasis on understanding both sorption and desorption processes as a means of understanding the sorption mechanisms. This work is directly aligned with the DOE BES Heavy Element Chemistry programs interests in understanding “the chemical and physical properties of these elements to determine solution, interfacial and solid-state bonding and reactivity”.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Functionalized Polymer Thin Films for Plutonium Capture and Isotopic Screening from Aqueous Sources

The rapid screening of plutonium from aqueous sources remains a critical challenge for nuclear nonproliferation efforts. The determination of trace-level Pu isotopes in water requires offsite sample preparation and analysis; therefore, new methods that combine plutonium purification, concentration, and isotopic screening in a fieldable detection system will provide an invaluable tool for nuclear safeguards. This contribution describes the development and characterization of thin polymer-ligand films for the isolation and concentration of waterborne Pu for direct spectroscopic analyses. Submicron thin films were prepared through spin coating onto Si wafers and consisted of combinations of polystyrene (PS) with dibenzoylmethane, thenoyltrifluoroacetone, and di(2-ethylhexyl)phosphoric acid (HDEHP). Pu uptake studies from solutions at pH from 2.3 to 6.3 indicated that only films containing HDEHP exhibited significant recovery of Pu. High alpha spectroscopy peak energy resolutions were achieved for PS-HDEHP films over a range of film thicknesses from 30 to 250 nm. Furthermore, a separate study was performed to evaluate uptake from a primarily Pu(V) solution where it was observed that doubling the HDEHP loading in the film increased uptake of Pu by an order of magnitude. X-ray photoelectron spectroscopy (XPS) analysis revealed that HDEHP was highly concentrated within the first few nanometers of the film at the higher loading. XPS analysis also revealed that, in the presence of water, HDEHP was stripped from the surface layer of the film at circumneutral pH. While significant losses of ligand were seen in all samples, higher loadings of HDEHP resulted in measurable amounts of ligand retained after a 12-h soak in water. Findings of this study are being used to guide the development of thin-film composite membrane-based detection methods for the rapid, fieldable analysis of Pu in water.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Impact of natural organic matter on plutonium vadose zone migration from an NH4Pu(V)O2CO3(s) source

Large amounts of plutonium produced at the Savannah River Site (SRS) in the latter half of the last century led to the release of plutonium to the subsurface. Low-level waste containing plutonium has also been disposed of in the SRS vadose zone. The mobility and risk posed by these plutonium sources is not well understood, in part, because of unknown interactions of the various mobile plutonium species with natural organic matter (NOM). This study investigated the influence of NOM on the behavior of plutonium(V) in the vadose zone through a combination of field lysimeter and laboratory studies. Well-defined solid sources of NH4PuVO2CO3(s) placed in 5-L lysimeters containing vadose zone soils NOM-amended or unamended were exposed to natural SRS meteorological conditions for three years. These lysimeters were removed from the field and analyzed using wet chemistry methods and X-ray absorption spectroscopy (XAS). Plutonium desorption from soils recovered from the lysimeters and laboratory batch sorption experiments using Pu-free soils both indicated that surface mediated reduction of Pu(V) to Pu(IV) was influencing Pu sorption behavior. For both lysimeters (amended and unamended with NOM), Pu migrated slowly through the lysimeter core, with > 95% of the Pu remaining within 2 cm of the source. However, without the NOM amendments, Pu was transported significantly farther than in the presence of NOM. Thus, the presence of NOM appeared to decrease the mobility. Working hypotheses to explain this behavior are that 1) formation of ternary surface-NOM-Pu complexes enhanced Pu sorption affinity causing less mobility and/or 2) formation of these ternary surface-NOM-Pu complexes prevented reoxidaiton of Pu(IV) to more mobile Pu(V) in the pore water.

plutonium, organic matter↗