Cermet Spent Nuclear Fuel Casks and Waste Packages
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0985-NN08-08
Cermet Spent Nuclear Fuel Casks and Waste Packages Charles W. Forsberg and Leslie R. Dole Nuclear Science and Technology Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831-6165 ABSTRACT Multipurpose transport, aging, and disposal casks are needed for the management of spent nuclear fuel (SNF). Self-shielded cermet casks can outperform current SNF casks because of the superior properties of cermets, which consist of encapsulated hard ceramic particulates dispersed in a continuous ductile metal matrix to produce a strong high-integrity, high-thermalconductivity cask. A multiyear, multinational development and testing program has been developing cermet SNF casks made of steel, depleted uranium dioxide, and other materials. Because cermets are the traditional material of construction for armor, cermet casks can provide superior protection against assault. For disposal, cermet waste packages (WPs) with appropriate metals and ceramics can buffer the local geochemical environment to (1) slow degradation of SNF, (2) reduce water flow though the degraded WP, (3) sorb neptunium and other radionuclides that determine the ultimate radiation dose to the public from the repository, and (4) contribute to long-term nuclear criticality control. Finally, new cermet cask fabrication methods have been partly developed to manufacture the casks with the appropriate properties. The results of this work are summarized with references to the detailed reports.
INTRODUCTION Spent nuclear fuel (SNF) casks are needed for storage, transport, and disposal. These casks may be designed for single or for multiple applications [1]. The functional requirements for SNF casks include (1) radiation shielding; (2) cooling of the SNF to limit its peak cladding temperatures; (3) physical protection; and (4) for disposal waste packages (WPs), delay of the radionuclide migration for long periods of time. Such casks may contain the individual SNF assemblies or canisters that contain multiple SNF assemblies. For example, in the United States, repository planning includes the development of a transportation, aging, and disposal (TAD) canister system. In such a system, a cermet-shielded cask might contain a TAD canister. Alternatively, the cask itself may be considered a shielded TAD canister, requiring minimal recycled overpacks to meet the specific requirements of storage, transport, and disposal. Overall cask performance is ultimately determined by the interactions and collective performances of cask materials of construction with the SNF and the storage, transport, and disposal environments. Shielded cermet casks have the potential to outperform all other SNF casks because cermets enable the incorporation of brittle ceramics with highly desirable properties within a high-thermal-conductivity strong ductile metal matrix. Figure 1 shows cermet cask construction. With advanced cermet manufacturing technologies, the cermet properties can be varied through the thickness of the cask wall to optimize material properties.
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