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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.
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.
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.
This proposal seeks start-up package funds and partial salary for a new tenure-track faculty position in level 3 probabilistic risk assessment (PRA) and/or radioecology within the Nuclear Environmental Engineering and Science (NEES) program at Clemson University. This faculty member would complement existing expertise in environmental radiochemistry and environmental health physics (EHP) while bringing skills that would allow the NEES faculty to tap into research funds that are currently beyond their reach. The ideal faculty candidate will have expertise in level 3 PRA which provides insight regarding the risks and consequences of nuclear related activities such as power plant production, waste disposal, and site remediation. The primary research activities of the ideal candidate will be to examine the transport, effects, and risks from environmental releases of radionuclides to human health and biota. R. A. Fjeld (Emeritus NEES faculty), N. A. Eisenberg (Emeritus NRC employee), and K. L. Compton (Ph.D. EEES (NEES) and current NRC employee) co-authored a textbook entitled: Quantitative Environmental Risk Analysis for Human Health, in 2007 which is just one of two textbooks in the field of level 3 PRA. Dr. Fjeld retired in 2009 and we are looking to fill this new faculty position with someone with similar expertise. There is a recognized worldwide need for educational programs focusing on nuclear science and technology due to the aging nuclear workforce and declining nuclear educational programs. European communities have recognized the need for similar research and educational programs and as a result have developed the Strategy for Allied Radioecology (STAR) Alliance (http://www.star-radioecology.org/). Similar efforts are underway in the United States through the National Center for Radioecology (NCoRE) managed by the Savannah River National Lab (SRNL) of which Clemson University is a key partner. With this grant the new faculty member will have the tools and support needed to develop a world-class research and educational program given the existing strengths in the current NEES program, the location of NCoRE close to Clemson University, and existing collaborations between current NEES faculty and SRNL scientists.
NEESRWM Director: Dr. Tim DeVol
Environmental Engineering and Earth Sciences | 342 Computer Court, Anderson, SC 29625 | (864) 656-1014