An Energy Frontier Research Center - FCC Will be Growing!
An Energy Frontier Research Center
Center for Performance and Design of Nuclear Waste Forms and Containers, WastePD
Gerald Frankel, Ohio State University, Center Director and Metals Team Lead
Jincheng Du, University of North Texas
Stephane Gin, CEA France
Seong Kim, Penn State University, Synergy Lead in Experimental Methods
Jie Lian, Rensselaer Polytechnic Inst., Ceramics Team Lead
Jenifer Locke, Ohio State University
Greg Olson, QuesTek Innovations, Synergy Lead in Design
Joe Ryan, Pacific Northwest National Laboratory
John Scully, University of Virginia
Christopher Taylor, Ohio State University
John Vienna, Pacific Northwest National Laboratory, Glass Team Lead
Jianwei Wang, Louisiana State University
Wolfgang Windl, Ohio State University, Synergy Lead in Computational Methods
The Office of Environmental Management in the US Department of Energy (DOE-EM) is responsible for management of defense wastes, including high-level tank wastes (HLW), that must be safely isolated from the environment for long periods. This requires understanding the performance and fundamental mechanisms of waste form degradation, and the design of new waste forms with improved performance, which comprise the goals of WastePD.
WastePD will develop innovative approaches and solutions to those goals through the synergistic interactions of individuals who are experts in the degradation behavior, modeling, and design of glasses, ceramics and metal alloys. WastePD is the first center ever created to address the degradation of this diverse group of materials in a comprehensive and coordinated manner. The science goals are grouped into three common topics: corrosion mechanisms via advanced characterization, environmental impacts, and materials design. The fundamental understanding of the degradation mechanisms of the waste forms and containers will allow DOE to develop new materials with improved properties, to prevent environmental contamination and to explore totally new disposal concepts. The waste forms of interest are tank waste transformed into glass, ceramic materials containing radionuclides, and metal canisters that protect the various waste forms.
The synergistic activities between the materials classes in the areas of experimental techniques, computational methodologies, and design approaches are a key component of WastePD. These synergistic activities will stimulate the achievement of new discoveries and reveal physical insights that would otherwise have been overlooked or not recognized. Sharing the understanding of the degradation mechanisms of glasses, ceramics, and alloys will lead to identification of commonalities and new materials design rules.
For organizational purposes, projects to address the degradation and design of waste forms are grouped into teams associated with the three materials classes. The Glass Team will develop a fundamental understanding of the structure and chemistry of the reacting glass-solution interface, determine the dominant mechanism of glass corrosion and the impact of environmental and chemical parameters, and develop methods to formulate high-performance glasses with tailored long-term performance. The Ceramics Team will develop a fundamental understanding of nano- to mesoscale phenomena including radionuclide incorporation, stability, transport, chemical corrosion, and surface interaction of ceramic waste forms upon near field interaction. New methods for ceramic waste form design will be developed with optimized waste loading, stability, and long-term performance. The Metals Team will investigate the fundamental aspects of alloying for controlling corrosion properties by focusing on bulk metallic glasses, high entropy alloys, and alloys that contain extremely high content of selected beneficial elements. It will also develop the mechanisms of stainless steel atmospheric pitting and cracking, and investigate the resistance of the newly developed alloys to storage and disposal conditions.
The schematic diagram in Figure 1 describes the organization of WastePD. The glass, ceramics, and metals teams are shown with the synergistic activities at the core. The management structure of WastePD is given in Figure 2.
The work scope is summarized in the following, based on the three materials classes: glass, ceramics and metals.
Much of the DOE-EM HLW currently exists as liquid, sludge or precipitated solids in temporary underground storage tanks. This waste will largely be isolated in a glass host before disposal. Accurate prediction of the performance of a disposal facility therefore requires understanding and control of waste glass corrosion over geologic time-scales. This remains a major challenge because of the very slow reactions that occur between two unstructured media that are far from equilibrium (glass and gel). Additionally, a series of coupled processes occurring at the nexus between water being the solvent and water being a solute are responsible for the overall rate of glass water reactions. It is only possible to understand and control glass corrosion through closely coupled theory, simulation, and experimentation. Improved understanding of the composition/structure effects on these processes would allow for rational design of glass waste forms with predictable long-term performance. The research will be conducted in three projects as shown in Figure 3.
Project G1: Rate-Limiting Mechanism of Glass Corrosion involves modeling and experiments on reference glasses to develop a fundamental understanding of the mechanism and a new kinetic model. The objective is to develop a fundamental understanding of mechanism(s) controlling the alteration of glass in the near-saturated conditions.
Project G2: Composition and Environmental Effects on Glass Corrosion Rate expands the testing of key rate limiting phenomena to determine the impacts of different glass compositions under a range of experimental conditions such as chemical and environmental parameters and glass composition. The scope will focus environmental parameters to those with the strongest impacts on the key mechanism from project G1.
Project G3: Rational Glass Design is focused on using the results from previous projects to develop and test models of long-term performance for use in design of waste glasses. This task will emphasize the development of tools for glass design with limited actual materials design and testing. Additionally, focus will be placed on the use of common approaches from the metals and ceramics teams and the modeling synergistic activities.
Not all of the DOE-EM wastes can be managed by bulk waste processing technology, as highly volatile radionuclides including 129I and 135Cs cannot be effectively incorporated into a borosilicate glass waste form. Single phase crystalline ceramics or multiphase assemblages have been investigated as alternative waste forms to borosilicate glass for HLW, excess plutonium from dismantled nuclear weapons, and minor actinides separated during fuel reprocessing. The ceramics team targets fundamental understanding of radionuclide incorporation, confinement and transport behavior in bulk crystalline ceramics and across solid-solid and solid-liquid interfaces that can be closely linked with the ceramic waste form degradation and stability under near field conditions. The approach taken in this research is summarized in Figure 4.
Project C1: An Integrated Computation and Experimental Approach in Designing Waste Forms and Tailoring Performance
An integrated approach will be used for synergizing atomistic computations in probing radionuclide incorporation and confinement coupled with experimental demonstration, enabling a science-based design of new crystalline ceramic waste forms. This is based upon our success in designing and synthesizing apatite-structure types for iodine incorporation. For a more coherent and focused research, model systems will be selected, e.g., apatite, hollandite, and perovskite as promising waste forms for critical fission products (Cs, Sr, and I).
Project C2: Degradation Mechanisms of Crystalline Waste Forms.
In this project, we will focus on the understanding of the long-term degradation/corrosion of ceramic waste forms for critical radionuclides in understanding their release mechanisms with or without ionizing radiation. It is envisioned that the ionization radiation upon decay of radionuclides could have significant impact on the phase, microstructure and degradation of crystalline waste forms. Leaching experiments will be performed on model systems to achieve mechanistic understanding of the release behavior of specific radionuclides. We will particularly focus on the interfacial behaviors across the solid-liquid (surface alteration) and solid-solid (heterogeneous/homogeneous boundaries) interfaces to elucidate the dominant degradation mechanisms (e.g., through radionuclide diffusion or dissolution). Experimental and simulation techniques applied to ceramics will include those applied to the other materials classes. The mechanistic understanding of the simple ceramic model system will be synergized with the knowledge achieved by the glass team to understand the complex behavior of the multiphase glass-ceramic assemblages.
Corrosion resistant alloys (CRAs) are used as materials of construction for canisters containing nuclear waste and have been proposed as waste forms for certain HLWs (e.g., pyrochemical metals and isolated 99Tc). CRAs are Fe- or Ni-based alloys that achieve their superior corrosion properties through the development of a thin protective surface oxide film, called a passive film. Unfortunately, CRAs are susceptible to rapid attack in the form of localized corrosion such as pitting, crevice corrosion, and stress corrosion cracking (SCC) under conditions where the passive film breaks down locally. Improved CRAs could alter the nature and performance of any storage or disposal facility. The metals projects will study CRAs and use Integrated Computational Materials Engineering (ICME) to develop new and improved CRAs. This has never before been attempted.
Project M1: Tailored Alloying in Corrosion Resistant Alloys (CRAs) and Development of New CRAs.
The goal is to develop the fundamental understanding underlying the corrosion resistance of CRAs through first principles, thermodynamic, and kinetic modeling, as well as experimentation. Approaches to increasing corrosion resistance through alloying will be addressed and the opportunities associated with the novel and tailored compositions and structures possible in Bulk Metallic Glasses and High Entropy Alloys will be investigated. The modeling will adopt DFT approaches and CALPHAD thermodynamic modeling to describe and predict the alloy microstructure as functions of composition and processing. The stability of passive films will be modeled using CALPHAD and localized corrosion will be addressed using a kinetic model informed by first principles calculations. Experiments will be aimed at a) providing guidance to the modeling efforts, b) testing alloy systems recommended by the modeling activities, and c) identifying the controlling factors and mechanisms governing the corrosion behavior of novel CRAs. Some of the experimental and simulation approaches will be common with the other two materials classes. The approach for this project is summarized in Figure 5.
Project M2: Atmospheric Pitting and Cracking of Stainless Steels.
This project will address the chemical and electrochemical attributes enabled by deliquescing environments on salt-contaminated SS during exposure in humid conditions; controlling factors in pit formation and transition to SCC; and development of cracks from pits generated by various exposure and metallurgical conditions. This project is tied to M1 by including the study of the new alloys developed in that project. The intent in starting examination in stainless steels is to select an alloy that will crack in a reasonable amount of time enabling the team to study the mechanism(s) driving atmospheric pitting, pit-to-crack transition, and H embrittlement. The project will also have a stronger focus on modeling. Specifically, results on stainless steel will be incorporated into DFT and Bayesian probabilistic models to enrich the understanding of the mechanisms driving pit-to-crack transition, hydrogen embrittlement, and possible failure in CRAs that will be investigated later in the project.
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