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Executive Summary T he Department of Energy’s Office of Environmental Management (DOE-EM) is responsible for cleaning up radioactive waste and environmental contamination resulting from five decades of nuclear weapons production and testing. A major focus of this program involves the retrieval, processing, and immobilization of waste into stable, solid waste forms for disposal. This report, which was requested by DOE-EM, examines requirements for waste form technology and performance in the cleanup program. It is intended to provide information to DOE-EM to support improvements in methods for processing waste and selecting and fabricating waste forms. The complete study task is shown in Box 2.1 in Chapter 2. This report focuses on waste forms and processing technologies for high-level radioactive waste, DOE’s most expensive and arguably most difficult cleanup challenge. The following key messages emerged from this study: • Two characteristics of waste forms govern their performance in disposal systems: (1) capacity for immobilizing radioactive or haz- ardous constituents and (2) durability. • U.S. laws, regulations, and other government directives and agree- ments under which DOE-EM operates are not all technically based, and none establishes specific requirements for waste form perfor- mance in disposal systems. The lack of waste form-specific perfor- mance requirements gives DOE-EM flexibility in selecting waste 1

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2 WASTE FORMS TECHNOLOGY AND PERFORMANCE forms for immobilizing its waste in consultation with regulators and other stakeholders. • Scientific and technical considerations have underpinned some DOE-EM waste form selection decisions in the past. Looking forward, DOE-EM has substantial opportunities to use advances in waste form science and technology to guide future selection decisions. • Waste form tests are used to ensure waste form production consis- tency, elucidate waste form release mechanisms, and measure waste form release rates. There is a need to demonstrate the application of current tests to new waste forms if they are to be used in the DOE-EM cleanup program. • Models of waste form performance are used to estimate the long- term (103-106 years) behavior of waste forms in the near-field environment of disposal systems. There could be significant benefits in providing more realistic safety and risk-informed analyses by improving existing models to capture the full complexity of waste form–near-field interactions. • Opportunities exist to develop more efficient waste form produc- tion methods and new waste form materials to reduce costs, expe- dite schedules, and reduce risks in the DOE-EM cleanup program. • Decisions on waste form development, testing, and selection are best made in a risk-informed systems context by considering, for example, how the waste form will be produced; what disposal environment it will be emplaced in; and how the waste form will function with other barriers in the multi-barrier disposal system to protect public health. • There is time during the remaining decades of the cleanup program to incorporate advances in scientific understanding of waste form properties and behavior and waste form production technology to achieve significant improvements in cleanup operations. DOE-EM should enhance its capabilities for identifying, developing where appropriate, and utilizing state-of-the-art science and technology on waste forms, waste form production processes, and waste form performance. These key messages are presented in 10 findings and 1 recommendation in the next chapter.