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The objective of this proposal is to define the potential source term of nanoparticles in natural systems to be used in a quantitative risk assessment. This will be achieved by quantifying the rate and extent of physical and chemical changes in nanoparticles during transitions from engineered to natural systems as indicated by the behavior of nanoparticles when released into natural waters.
Approach: Specific objectives of this project will be to:
The results of this work can be used to inform risk analysis by identifying the nanoparticles likely to be mobile in natural environments and biologically available in natural waters. In addition, the following tools will be developed to determine the fate of nanomaterials in natural systems:
All the data produced in this project will be released to public databases. The developed models will be automated for high throughput screening.
As part of the broader impact of this work, we propose to create an Undergraduate Creative Inquiry (UCI) research group at Clemson. UCI is a Clemson wide focus on team-based undergraduate research that transcends both class and discipline. We shall recruit motivated undergraduate students from all disciplines, especially those in the PI’s departments of Environmental Engineering and Earth Science, Chemical and Biomolecular Engineering, and Material Science and Engineering. We will employ an application process to target a group of eight students at different stages in their education with priority given to women and minority students. Ideally we will have a diverse group of undergraduate researchers recruited as freshmen and sophomores and continuing up to their graduation.
Objective: The objective of this work is to quantify interactions of risk driving radionuclides with engineered barrier materials used in radioactive waste repositories. The engineered solids to be examined will be iron oxide byproducts of steel corrosion and bentonite clays as representative backfill materials. Data examining sorption and ion exchange of various radionuclides to these materials are available. However, data are lacking for studies at high temperatures and high ionic strengths. The high ionic strength is expected to limit sorption of cations due to competition for a finite number of sorption and/or exchange sites. However, as temperature increases, sorption of actinide ions is hypothesized to increase based on an entropy driven displacement of solvating waters. Therefore studies at extremely high ionic strengths and at high temperatures are necessary. We will use a suite of actinide ions in these experiments to allow for a systematic and quantitative understanding of ion interactions with these materials as a function of ion size, hydration state, and charge. The deliverable will be a qualitative conceptual model and a quantitative thermodynamic aqueous/surface complexation speciation model describing actinide sorption to engineered barrier materials, which is based upon a mechanistic understanding of specific sorption processes as determined from both micro-scale and macro-scale experimental techniques.
Hypotheses: The overarching hypothesis of this research is that strong actinide interactions with metal (oxyhydr)oxide surfaces are manifested by large stability constants for the actinide surface complexes. These large stability constants are due to positive entropies which are mechanistically driven by displacement of solvating water molecules from the actinide ion and the mineral surface during sorption and/or surface precipitation. Such entropies are accessible through measurement of sorption enthalpies and stability constants using surface complexation modeling and calorimetric titration techniques. Additional specific hypotheses that are corollaries to this general hypothesis are:
Outcomes: This work directly addresses the expressed need in Technical Work Scope Identifier FC-6 for understanding “aqueous speciation and surface sorption at high temperature and high ionic strengths anticipated in near field conditions.” The primary deliverable will be a set of thermodynamically based sorption and ion exchange constants describing radionuclide sorption to engineered barrier materials. These data will provide an understanding of the fundamental reaction mechanisms occurring at the mineral-water interface. A greater understanding of these processes will reduce the uncertainty in strategies for sequestration of radionuclide bearing wastes. Overall this project will increase our understanding of radionuclide interfacial reactions and help to ensure human and environmental health are protected during treatment and disposal of radionuclide bearing wastes.
A major scientific challenge in environmental sciences is to gain the scientific knowledge needed to reliably predict and control the cycling and mobility of actinides (e.g.,. plutonium). Over 2000 metric tons of plutonium (Pu) have been deposited in the surface-subsurface worldwide. This along with its long-half life and toxicity, represents a significant long-term environmental risk. Currently, we cannot reliably predict how Pu will move once deposited in the subsurface preventing accurate assessment of risk to human health. Field measurements document Pu transport kilometers farther than models predict. Significant gaps in our current understanding of the dominant biogeochemical (inorganic, organic, and microbial) processes that control actinide transport exist. A mechanistic understanding of the surface structure and reactivity of coupled Pu-mineral, Pu-organic ligand, and Pu-microbe interfacial processes is needed to advance our understanding of the fate and transport of Pu in this complex subsurface system.
Our program focuses on identifying and quantifying the dominant biogeochemical processes that control the behavior of Pu in the subsurface. Despite the recognized importance of colloid-facilitated transport, very little is known about the mechanisms controlling the coupled Pu-colloid interfacial processes and associated reaction rates. Equally uncertain are the conditions under which colloid-facilitated transport is not significant. The objective of this research program is the identification and quantification of Pu-biogeochemical processes such as:
on the affinity and sorption/desorption rates of Pu over a range of environmentally relevant concentrations (10-8 to 10-18 mol/L). With the use of unique capabilities at LLNL, such as accelerator mass spectrometry, an IsoProbe mass-spectrometer, a Titan Transmission Electron Microscope, a nano-secondary ion mass spectrometer, nuclear magnetic resonance facilities, and high-performance computing capabilities, we will test whether the biogeochemical processes identified, operate over a 10 order of magnitude range in concentration. New knowledge gained as a result of this work will provide foundational science for the prediction and control of Pu mobility in the surface/subsurface.
The objectives of this project are to design and test an alternative sample loading method for thermal ionization mass spectrometry (TIMS) analysis. TIMS is one of the most sensitive analytical tools for determining isotopic ratios for plutonium and uranium and is used widely within the nuclear nonproliferation and safeguards communities. This work seeks to introduce a polymer thin film based method for loading samples that would replace the traditional ‘bead loading’ method. This thin film system has the potential to decrease sample preparation time, increase sensitivity, and minimize the risk of sample loss due to explosive decompression commonly observed using the current bead loading technique.
The project team has extensive experience in radioisotope detection and measurement, radiochemical separations, and the surface engineering technologies required to produce the thin films to be utilized in this work. Here is a summary of methods to be employed by this team:
Thin film coating: Degassed rhenium ribbons will be coated with a thin film of type 1 strong anion-exchange polymer. Polymer thin films will be deposited on the ribbons using a dip-coating method. The experiments will focus on elucidating the impacts of solvents, polymer solution concentration, and dip-coating withdrawal speed on film thickness. A theoretical framework for thin film formation will be used to guide experimental design. Characterization will verify uniform coating of rhenium ribbons by the polymer films and will determine their thickness values.
Sample loading: These experiments will examine methods for loading uranium and plutonium from solutions onto the ribbons, determine the uptake kinetics, and determine loading capacities. Three methods will be used to load uranium and plutonium onto the coated ribbons: Static batch uptake experiments, flow-through uptake in continuously stirred batch reactors, and microvolume additions directly to the ribbon.
TIMS analysis: A side-by-side comparison of traditional bead-loaded materials and thin film-loaded samples will be performed at SRNL. The analysis will be performed using a reference plutonium sample, examining both the isotopic ratios and the total counts obtained for each sample. These studies will allow determination of any signal enhancement created by the alternative loading method and potentially indicate reduction of sample loss due to explosive decompression.
Ribbon geometry: After optimal thin film formation and loading conditions have been determined, the research will focus on fabrication and testing of ribbons with novel rhenium physical geometry. The varying geometries may result in greater ionization of plutonium during the TIMS analysis.
The primary deliverable from this project will be a method for producing polymer thin film-coated rhenium ribbons to improve TIMS analyses. The knowledge gained from these studies has the potential to increase the sensitivity of TIMS analyses by one or more orders of magnitude. Increasing the sensitivity of TIMS analyses may lead to enhanced ability to detect proliferant isotopes. The results from this project will be disseminated to the scientific community in the form of progress reports to NNSA, technical presentations at national meetings, and publication of the results in peer-reviewed literature.
Fellowships are requested to support three graduate students (MS/PhD) per year in nuclear environmental engineering and science (NEES) program within the Environmental Engineering and Earth Sciences Department at Clemson University. Fellowship students will pursue a course of study in either Environmental Health Physics (ABET-ASAC accredited at MS level) or Environmental Radiochemistry. Fellows will conduct their thesis/dissertation research in collaboration with an outside partner such as a national laboratory, utility, or regulatory agency. This will provide fellows with an opportunity both to interact with a practicing professional and to conduct research that contributes to the solution of a contemporary technical issue in the nuclear sector.
The NEES program is a graduate only academic program established in the early 1980’s. The program focuses on the environmental aspects of nuclear technologies, including environmental health physics, radioactive waste processing, environmental risk assessment, the nuclear fuel cycle, radiation detection and measurement, environmental radiochemistry, and environmental remediation. The average number of M.S. and Ph.D. students pursuing a program of study in the NEES focus area has been ~14 per year over the past 5 years. There has been a significant increase to where there are currently 23 M.S. and Ph.D. students within the NEES concentration.
The objective of this research is to advance scientific understanding in the development of high-selectivity sensor materials, high-sensitivity sensors, and data analysis techniques for ultra-trace-level quantification of radionuclides, particularly α- and β-emitting radionuclides. An on-line system for ultra-low-level detection of α- and β-emitting radionuclides in environmental media (water, air and sewage) would be a powerful nuclear forensics tool. Currently, no such system is available.
Scintillators are unique materials that transform high energy ionizing radiation into detectable visible light, being used for the detection and measurement of radiation in security, energy, medical diagnosis, and other strategic fields. Presently, there is a knowledge gap relating the fabrication and processing conditions of transparent ceramic scintillators with their scintillation output, a situation that negatively impacts the widespread use of these materials, as well as undermines their performance. We hypothesize that the intensities of scintillation and afterglow are related to the concentration of structural imperfections that generate electronic traps, and that it is possible to mitigate afterglow by identifying suitable rare earth (RE) dopants to drain charge carriers off the traps. In order to evaluate the above hypothesis, it is proposed to:
The innovative aspect of the proposed research is to go beyond the fabrication of transparent ceramics to establish relations between fabrication conditions, microstructure and defect characteristics with afterglow and scintillation performance, and to develop a predictive capability to identify RE dopants to mitigate afterglow. The project will focus on RE-doped Lu2O3, Y2O3, and Y3Al5O12 transparent ceramics.
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