Specialized Disposal Sites for Different Reprocessing Plant Wastes
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Specialized Disposal Sites for Different Reprocessing Plant Wastes Charles W. Forsberg1, and Michael J. Driscoll2 1 Nuclear Science and Technology Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831 2 Department of Nuclear Science and Technology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139 ABSTRACT Once-through fuel cycles have one waste form: spent nuclear fuel (SNF). In contrast, the reprocessed SNF yields multiple wastes with different chemical, physical, and radionuclide characteristics. The different characteristics of each waste imply that there are potential cost and performance benefits to developing different disposal sites that match the disposal requirements of different waste. Disposal sites as defined herein may be located in different geologies or in a single repository containing multiple sections, each with different characteristics. The paper describes disposal options for specific wastes and the potential for a waste management system that better couples various reprocessing plant wastes with disposal facilities.
INTRODUCTION The United States is considering the reprocessing of SNF; thus, it is appropriate to consider the implications of reprocessing on repository design. While SNF is a single waste form, reprocessing creates multiple waste forms. Because reprocessing plant wastes are engineered waste forms that usually contain radionuclides with similar chemical characteristics, the waste forms can be potentially matched with specific disposal environments to minimize waste management costs and risks. Reprocessing plants produce multiple streams that may include (1) uranium; (2) plutonium; (3) minor actinides (MA); (4) high-heat radionuclides (HHR) containing 137Cs and 90Sr with their decay products; (5) volatiles and their subsequent decay products that would be released during reprocessing operations including inert gases (He, Ne, Ar, Kr, Xe, and Rn), halogens (F, Cl, Br, I), hydrogen, nitrogen, and carbon; (6) the remaining radionuclides that are low heat radionuclides (LHRs), and (7) structural materials such as zirconium clad from LWR SNF. Table I shows these categories and their heat generation rates as a function of time [1]. While SNF contains hundreds of radionuclides, in any repository only a few radionuclides determine the risk to the public and thus control repository design. For example, Fig. 1 shows the expected radiation doses to the public [2] from the proposed Yucca Mountain (YM) repository versus time. The analysis indicates that 99Tc and 129I control the maximum dose to the public over time. If SNF is reprocessed and these radionuclides are naturally or deliberately separated from the other wastes, serious consideration should be given to developing methods that can better isolate these radionuclides from the biosphere. If these radionuclides can be better isolated from the environment, the risk to the public is decreased and repository capacity (based on allowable radionuclide releases from the rep
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