disposal. In the last case—which follows if the uranium fraction is deemed to be a waste stream —additional processing steps (for example, oxidation) would be required.

An issue with respect to the uranium metal fraction is that some of it is enriched. ANL has indicated plans for blending this material down to low enrichment levels in order to minimize proliferation concerns.

TRU METAL FRACTION

The electrometallurgical process would generate a separate TRU metal fraction composed of approximately 30% uranium by weight, with the remaining mass composed of unfractionated actinides, primarily plutonium, and some of the rare-earth elements from the processed fuel. As a reactive metal, it is unlikely that this fraction would be acceptable for direct geologic disposal, so that either interim surface storage or additional treatment for disposal would be required.

Deep geologic repositories are the internationally preferred option for disposal of high-level waste (HLW) because associated release of radiation to the biosphere would be unlikely. This characteristic is important because the generally accepted standard of risk for public exposure to radioactivity is expressed in terms of radiation doses1 that are calculated by taking into account actual pathways from repository to biosphere, and their likelihoods, when estimating the probabilities of radionuclide releases to the biosphere.

While removal of actinides from the waste stream might result in a reduction in the volume of waste bound for storage in a geologic repository,2 removal of actinides appears to yield little accompanying reduction in the overall risks from the repository. This is because, in evaluating the comparative radiation dose risks associated with actinides as compared to fission products in HLW, safety analyses by international repository programs3 and for the U.S. HLW repository4 suggest that long-lived, soluble, weakly sorbed fission products (e.g., Se-79, Tc-99, I-129) would dominate the long-term dose risk.

An emerging alternative for disposal of the TRU metal fraction, mentioned by ANL toward the end of this study but not considered in detail by the committee, would involve a modification of the electrometallurgical process such that the TRU metal fraction would not be deposited electrolytically in a cadmium cathode. Instead, the TRU metal fraction would be incorporated into the zeolite waste fraction, described below.

1  

L.C. Hebel et. al., 1978, Rev. Mod. Phys., 50(1), Part II.

2  

Ibid.

3  

See, e.g., NAGRA, 1985. “Project Gewahr 1985/Nuclear Waste Management in Switzerland: Feasibility Studies and Safety Analyses,” NGB 85-09, National Cooperative for the Storage of Radioactive Waste, Baden, Switzerland; SKB 91: “Final Disposal of Spent Nuclear Fuel. Importance of the Bedrock for Safety, ” Swedish Nuclear Fuel and Waste Management Co., Stockholm, Sweden; YJT, 1992, “Final Disposal of Spent Fuel in the Finnish Bedrock: Technical Plans and Safety Assessments,” YJT-92-31E, Nuclear Waste Commission of Finnish Power Companies (YJT), Helsinki, Finland.

4  

Electric Power Research Institute, 1992, “Demonstration of a Risk-Based Approach to High-Level Repository Evaluation: Phase 2,” EPRI TR-100384, Electric Power Research Institute, Palo Alto, Calif.; “Total-System Performance Assessment for Yucca Mountan —SNL Second Iteration (TSPA-1993),” SAND93-2675, Sandia National Laboratories, Albuquerque, N. Mex.



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