Application of the TSPA Glass Degradation Model to Non-Conforming Waste Forms
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Application of the TSPA Glass Degradation Model to Non-Conforming Waste Forms W. L. Ebert Chemical Engineering Division, Argonne National Laboratory, Argonne, IL 60439 [email protected] ABSTRACT An approach is presented for determining if the models used to calculate the release of radionuclides from defense high-level radioactive waste (HLW) glass for total system performance assessment (TSPA) calculations can be used to account for the release of radionuclides from waste forms other than standard borosilicate glasses. The fractional release rates of radionuclides due to waste form degradation, the available surface area, and the radionuclide inventory in an alternative waste form can be compared with the corresponding models used in TSPA for HLW glasses to determine if those models adequately represent the waste form. This approach is demonstrated for the ceramic and metallic waste forms developed for electrometallurgically treated spent sodium-bonded nuclear fuel. Depending on the waste form, comparisons made with aspects of the HLW glass model may be based on similarities in degradation mechanisms or purely empirical.
INTRODUCTION Borosilicate glass is being used to immobilize high-level radioactive waste (HLW) by direct vitrification for disposal in the Yucca Mountain repository. Borosilicate glass waste forms that are being made (or will be made) with tank wastes at U.S. Department of Energy (DOE) facilities at Savannah River, West Valley, and Hanford are generally homogeneous glasses with less than 1% crystalline phases that are made in Joule-heated melters at about 1150ºC. Requirements for accepting these HLW glass waste forms for disposal in the repository are contained in the Waste Acceptance System Requirements Document (WASRD) [1], which establishes minimum performance levels for waste forms and identifies information needed to support the design and evaluation of the disposal system. Although borosilicate glass will be used to immobilize the vast majority of HLW, alternative waste forms have been developed for several waste streams that are either not amenable to direct vitrification or require special processing to increase waste loadings. Because they differ from the standard borosilicate HLW glass addressed in the WASRD, these are referred to as “non-conforming waste forms”. Waste form producers must demonstrate that non-conforming waste forms comply with the WASRD and are acceptable for disposal. Although acceptance criteria for non-conforming waste forms are not addressed specifically, it is reasonable to use the requirements developed for HLW glass to show non-conforming waste forms are compliant. The same methods used for HLW glasses may be applicable to non-conforming waste forms in some cases, while alternative methods may be needed to show compliance with other requirements. Probably the most important issue to be addressed for non-conforming waste forms is how to account for their impact as a source of radionuclides in total system performance assessment (TSPA) calculations. The TSP
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