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OCR for page 27
ELECTROMETALLURGICAL TECHNIQUES FOR DOE SPENT FUEL TREATMENT: An Assessment of Waste Form Development and Characterization 4 Additional Considerations Related to the Demonstration Project In addition to the testing and ultimate fate of the metal and ceramic waste forms, there are additional considerations related to ANL' s demonstration project that are associated with the issue of waste forms. DISPOSITION OF THE URANIUM PRODUCT STREAM PRODUCED BY THE EMT PROCESS As stated previously, the uranium-metal stream is considered to be a product stream that would be incorporated into the nation's enriched-U inventory. Two uranium stream products will be produced—fuel highly enriched (60 to 65%) with U-235, and blanket elements made from depleted uranium but that have been in the reactor for close to two decades and thus have a buildup of plutonium and some fission products. It is not now clear where either stream will ultimately go. The fuel uranium will be diluted down to 19% 235U before it is cast into uranium ingots. The 1996 Environmental Impact Statement1 says that this highly enriched uranium (HEU) will be disposed of by one of two means: Conversion to low-enriched uranium (LEU) light water reactor fuel, or Disposal as low-level waste (LLW) after blending down to 0.9% 235U. Conversion to LEU fuel, by dilution to 4.8% 235U, would still leave a product that would have orders of magnitude more Pu-Np, and more fission products (FP) than the ASTM acceptance standard for LEU fuel. Thus this would not be acceptable without further processing to remove Pu and FP. Disposal as LLW after blending down with depleted uranium (perhaps about 0.25% 235U) to 0.9% would produce a product with about 40 nCi/gram of transuranic (TRU) waste activity and thus under the limit of 100 nCi/gram required for LLW. It would also require that the volume of the uranium waste be increased by a factor of about 100. ANL is proposing that the blanket elements also be run through the electrometallurgical process to produce a metal stream that is mostly depleted uranium. It is not clear yet whether the process can produce depleted uranium of <100 nCi/gram of TRU. There will also be a ceramic waste form comparable to that produced from the fuel. ANL believes it is feasible for the TRU-bearing depleted uranium to be accepted in the Waste Isolation Pilot Plant (WIPP). However, it has no approval for this and there is some question of whether this would meet the “defense waste” criterion required for WIPP. Staff of the EMT Program have discussed applicable product purity levels with the staff of the Oak Ridge National Laboratory Y-12 Plant for Y-12 acceptance of the uranium metal.2 Typically low-enriched uranium ingots from the program significantly exceeded the Y-12 acceptance criteria. If DOE decides that a commercial disposition 1 Environmental Assessment: Electrometallurgical Treatment Research and Demonstration Project in the Fuel Conditioning Facility at Argonne National Laboratory-West, DOE/EA-1148, U.S. Department of Energy Office of Nuclear Energy Science and Technology, Washington, D.C., 1996. 2 Private communication, Harold McFarlane, ANL-W.
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ELECTROMETALLURGICAL TECHNIQUES FOR DOE SPENT FUEL TREATMENT: An Assessment of Waste Form Development and Characterization option is desirable, some additional purification must be sought. To date, these options have not been studied. QUANTITY OF EMT WASTE FORMS PRODUCED FROM EBR-II SPENT NUCLEAR FUEL The committee notes that both the quantity and radionuclide inventory of EMT waste forms are extremely small relative to those for commercial SNF and DHLW. The DOE should evaluate whether small quantities, both in terms of volume and radionuclide inventory, of novel waste forms should be characterized and qualified to the same level of detail as major waste forms. For example, issues such as variability in the burn-up of commercial SNF or uncertainty in the fraction of volatile fission products at the matrix-cladding gap of SNF may lead to greater impacts on repository safety than a simple and demonstrably bounding analysis of performance by the MWF and the CWF. However, because final qualification criteria have not been set, it is difficult to assess whether the testing is excessive or not at this stage. Conclusion: Alternative, conservatively bounding strategies for assuring safe disposal of such relatively small quantities of novel HLW may result in significant cost avoidance while still protecting public safety. However, if the EMT process were to be proposed or considered for processing of other DOE SNF (e.g., N-Reactor fuel at Hanford), then a full qualification of EMT waste forms for repository disposal would be required by DOE prior to any final approval and implementation of the EMT process for this extended purpose.
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