Electrometallurgical Techniques for DOE Spent Fuel Treatment An Assessment of Waste Form Development and Characterization (1999) / Chapter Skim
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3 Waste Form Qualification and Acceptance
3 Waste Form Qualification and Acceptance
Pages 13-26
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From page 13... ...
waste forms must be assessed within a system context of overall repository safety. The committee recognizes that while general specifications have been identified for acceptance of DOE spent filed and waste forms into the repository program,2 explicit criteria for evaluating such waste forms under relevant repository conditions are not yet available.
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To support a final waste-acceptance decision, however, major qualification and characterization activities will continue beyond the end of the demonstration project. To date, both commercial spent fifed and vitnfied defense HEW have been subjected to detailed characterizations conducted with respect to their performance in a geologic repository.7 Such characterization data for borosilicate glass have been used to guide isolation strategies as well as initial design of engineered barrier systems to assess the viability of a geologic repository.8 At present, only DOE SNF is being grouped by RW with respect to common characteristics.
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: The documentation prepared by a HEW producer describing planned analyses, tests, and engineering development work to be undertaken, as well as ~nfom~ation to be included in waste-form production records to demonstrate compliance of the proposed waste form with waste acceptance specifications. Waste Form Qualification Report (WQR)
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a strategy appropriately based on RW's waste acceptance criteria for the characterization of its MEW and CFW for eventual acceptance by RW. This strategy encompasses its characterization protocols, including short-tenn test procedures, for its ceramic and metal waste forms.
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development. Research at ANL-E has evaluated alloy metallurgy and alloy properties, including mechanical properties, thermophysical properties, and corrosion behav~or.~7 The corrosion resistance of SS-ISZr alloys has been determined using immersion tests, electrochemical tests, and accelerated corrosion tests (vapor hydration, high temperature immersion, and product consistency tests)
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No data have been presented to the committee thus far for "standard" SS-15Zr samples. ANT personnel did discuss corrosion testing of SS- ~ SZr MWF samples at a 1998 meeting, concluding that "SS-Zr waste forms are very resistant to the normal corrosion conditions envisioned at the proposed Yucca Mountain geologic repository."22 Conclusion: Corrosion behavior data for the SS-15Zr MWF standard need to be oblainetl.
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Recommendations: Instead of continuing to conduct a large number of corrosion tests using mild conditions, it would be better to subject a few carefully selectee! samples to additional evaluation by surface analysis to determine the chemical composition of the corrosion products.
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Develop metal waste specifications that are based on performance characterization results of small samples with variations in the pnncipal constituents: zirconium, uranium, technetium, plutonium, neptunium, and noble metals. Determine performance characterization with electrochemical techniques, corrosion tests, vapor hydration tests, arid attribute tests.
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26 National Research Council, Electrometallurgical Techniques for DOE Spent Fuel Treatment: Spring 1998 Status Report on Argonne National Laboratory's R&D Activity, National Academy Press, Washington, D.C., 1998, pp.
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Finding: ANE's tests of several months' duration indicate that the CWF dissolves at a rate equal to or less than that of the reference DHEW borosilicate glass. Conclusion: If dissolution remains the dominant release mechanism uncler actual repository conditions, then the release performance of the CWF will be at least comparable to that of DHEW borosilicate glass.
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The EMT Program's waste-fonn qualification program is based on adaptation of models arid test protocols developed for DHEW borosilicate glass. 36 Sodalite is the name of a group of alum~no-silicate framework materials fanned by linkage of SiO4 and A1O4 tetrahedra Mat form internal cavities that can be occupied by chloride or other anions.
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Furthennore, the formation of nanocrystals of plutonium oxide after fabrication of the CWF raises questions as to whether plutonium might be released through a geologic repository system as plutonium oxide colloids rather than as dissolved plutonium. Fabrication of Ceramic Waste Forms HIP has been adopted as the reference technology for densification during the demonstration program.
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These criteria and associated work to date are as follows: Criterion Goal 2~. Develop ceramic waste specifications that are based on perfonnance characterization results of samples with principal constituent variations: glass fission products, uranium and plutonium.
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When criteria for acceptance of waste forms for geologic repository placement are adopted by RW, test procedures for the waste forms produced by the electrometallurgical process may require modification. The committee believes, however, that the test procedures used for the MWF and CWF are appropriate for the completion of ANt's demonstration project.
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