Electrometallurgical Techniques for DOE Spent Fuel Treatment Final Report (2000) / Chapter Skim
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Executive Summary
Executive Summary
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Electrometallurgical technology was suggested as a means to produce the same waste forms for all of the spent fuels in the DOE inventory, thus providing substantial cost savings for qualification of these waste materials for disposal in a geologic repository. Electrometallurgical technology (EMT)
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THE ELECTROMETALLURGICAL PROCESS AT ANL The electrometallurgical treatment process for spent fuel at ANL consists of several distinct steps: chopping the fuel elements, electrorefining the driver and blanket fuel, removing entrained salt from uranium electrodeposits and consolidating dendritic deposits in a cathode processor, casting separately into ingots the uranium metal from the cathode and the metal residue from the anode, and, finally, mixing, heating, and pressing the salt electrolyte with zeolite to form a ceramic waste. The electrorefining step is the heart of the EMT process.
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Alternatives to Electrometallurgical Technology for Treatment of DOE SNF In two of its reports the committee, as part of its fulfillment of its tasks, evaluated alternatives to electrometallurgical technology:9 l0 direct disposal, glass material oxidation and dissolution, melt and dilute, PUREX, 9National Research Council, An Assessment of Continued R&D into an Electrometallurgical Approach for Treating DOE Spent Nuclear Fuel, National Academy Press, Washington, D.C., 1995. In this report the committee considered spent fuel treatment alternatives to EMT within the context of all DOE SNF.
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However, the committee noted in its seventh report that public concern regarding transport of EBR-II spent fuel to the PUREX facility at the Savannah River site (SRS) , combined with the expected shutdown of the PUREX canyons at SRS, argues against this alternative.l1 WASTE STREAMS PRODUCED BY THE EMT PROCESS Waste Form Qualification The DOE, through its Office of Civilian Radioactive Waste Management (DOE-RW)
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should be continued in the post-demonstration phase for selected samples to determine the chemical composition of passivating films and/or corrosion products. According to ANL personnel in presentations to the committee,l8 galvanic corrosion tests according to ASTM G71 have indicated that enhanced corrosion of SS-15Zr due to galvanic coupling of the MWF with the inner lining of the waste form container (assumed to be alloy C22)
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Accelerated alpha damage testing was carried out on simulated CWF doped with 0.2 to 2.5 wt % 238Pu or 239Pu. Initial results from this ongoing study show no significant degradation of the waste after 6 months at relatively low doses.22 Recommendation: The electrometallurgical technology program should continue to investigate and evaluate in the post-demonstration period whether the test protocols and conceptual models developed for monolithic single-phase borosilicate glass can adequately represent the behavior of the nonhomogeneous multiphase CWF.
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POST-DEMONSTRATION ACTIVITIES If DOE chooses to use the EMT process to treat sodium-bonded SNFs in the DOE inventory, or any other spent fuels,24 ANL must complete all the activities required to qualify both the metal and ceramic waste baseline forms for repository disposal. ANL-E must also provide ongoing technical support to operations at ANL-W, and ANL-W must complete the required facility modifications and qualify the new, larger-scale equipment needed to handle the increased volume of fuel.
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Recommendation: If the DOE decides to treat the remaining sodium-bonded spent fuel inventory and the waste form qualification efforts are successful, the required equipment upgrades and facility modifications should be adequately funded to ensure that treatment can be completed in a reasonable time and at a reasonable cost. The use of pressureless sintering to produce the ceramic waste form can offer distinct advantages over the baseline HIP process.
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Finding: The volume of sodium-bonded spent fuel waste generated using the "throw away salt" option, where a portion of the plutonium and fission-product-contaminated salt is mixed directly with zeolite and glass particles for waste disposal, is such a small fraction of the total waste destined for geologic disposal that waste volume reduction resulting from the use of the zeolite column would not have a significant impact on the overall waste disposal problem. Recommendation: Continued development of the zeolite column should not be considered a high priority unless a compelling argument can be made that its development and implementation would significantly reduce waste disposal costs or associated costs of EMT treatment of the DOE sodium-bonded spent fuel inventory.
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The total quantity of EBR-II spent nuclear fuel is relatively small, particularly in comparison to the total DOE spent fuel inventory, so even if qualification of the waste form were to prove impossible, the quantity of these materials that had been produced would be modest. The committee has found no significant technical barriers to the use of electrometallurgical technology to treat EBR-II spent fuel, and EMT therefore represents a potentially viable technology for DOE spent nuclear fuel treatment.
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