Electrometallurgical Techniques for DOE Spent Fuel Treatment: Spring 1998 Status Report on Argonne National Laboratory's R & D Activity (1998)

The Committee on Electrometallurgical Techniques for DOE Spent Fuel Treatment has now entered the third phase of its activity, and its task has evolved in accord with progress made by Argonne National Laboratory (ANL)¹ in its research and development program for electrometallurgical technology (EMT). The U.S. Department of Energy (DOE) asked the National Research Council to focus on specific aspects of the original charge during the third phase of the committee's work (Appendix A). In this report the committee addresses the three aspects of its charge. The first is to monitor the scientific and technical progress of the ANL program on EMT for the treatment of DOE spent nuclear fuel. The second is to examine the viability of electrometallurgical treatment technology in light of technical progress in other possible treatment technologies. The DOE requested that the committee identify significant technical advances that might have occurred since the committee's 1995 report,² with the specific focus on advances that might offer a preferred approach to the treatment of the EBR-II spent fuel that will remain at the completion of the demonstration. The third part of the revised charge to the committee is an evaluation of criteria by which the success of the demonstration project will be judged. These criteria were developed by DOE and ANL in response to an earlier recommendation by this committee.³

The ANL program on electrometallurgical treatment technology is now focused exclusively on the use of EMT for treatment of Experimental Breeder Reactor II (EBR-II) spent nuclear fuel. Consequently, the committee's evaluation of the demonstration project has that same focus. No other spent fuels in the DOE inventory are to be treated as part of the demonstration project, and therefore this report does not address the use of EMT for any spent fuels other than EBR-II fuel. A similar focus exists in the evaluation of alternative treatment technologies.

Since the committee's last site visit in October, 1996, ANL-West (ANL-W) has continued its efforts toward characterizing and optimizing the operating conditions for the Mark-IV electrorefiner (ER). These efforts to date have been conducted while meeting the scheduled throughput for processing two irradiated EBR-II driver assemblies, on average, per month. Efforts at ANL-W are also focused on determining the optimum conditions for maximizing uranium dissolution at the anode while minimizing zirconium dissolution. The Mark-V ER as of the site visit was installed in the argon atmosphere cell and is undergoing shakedown. High-throughput electrorefiner (HTER) development continues to be a focus at ANL-East (ANL-E). With regard to potentially processing N-reactor fuel, the HTER under development must be capable of efficiently separating uranium and zirconium. Preliminary experiments resulted in achieving the goal of 98.5 percent removal of uranium from the anode basket to the cathode but fell short by 5 percent of retaining 80 percent of the zirconium in the anode basket.

ANL-E has prepared and delivered to ANL-W the UCl₃ needed for the Mark-V ER. ANL-W has completed the processing of 48 of 100 driver assemblies. It has cast 372 kg of low-enrichment uranium. The cathode processor size has increased from 12 to 17 kg. The casting furnace batch size has increased from 36 to 54 kg. Blanket fuel element chopper installation is complete. The Mark-V ER is installed and process chemicals loaded.

ANL has documented two important decisions: (1) the selection of sodalite over zeolite as the host ceramic waste form for nonnoble fission products and transuranic element (TRU) waste components from the molten processing salt of the EMT process and (2) an outline of a qualification testing plan for both the proposed ceramic and metal waste forms. At ANL-E, “cold” metal waste forms using simulated, nonradioactive fission products are being produced and studied. A number of ongoing activities are related to developing the glass-bonded sodalite (GBS) ceramic waste form. Establishing the credibility of the EMT process must eventually include resolution of waste form issues.

Detailed descriptions of the following technologies are discussed in the body of this report. This summary gives an assessment of the viability of these technologies as possible alternatives to electrometallurgical treatment for EBR-II spent fuel.

The long-term durability of the proposed overpack container has not been demonstrated or documented. At the present time, direct emplacement of EBR-II spent nuclear fuel (SNF) is precluded by DOE policy concerning acceptance of the Resource Conservation and Recovery Act (RCRA)-designated mixed waste (which contains both hazardous and radioactive waste). Because it contains both metallic uranium and sodium, EBR-II SNF is categorized as a RCRA hazardous waste that is potentially both pyrophoric and reactive.

Considering the time period and cost necessary for developing a Glass Material Oxidation and Dissolution System (GMODS) relative to the level of maturity of the EMT process, GMODS does not appear to be a viable alternative for processing only EBR-II SNF unless the process is also applied to other SNFs and miscellaneous fissile materials.

No experimental work relevant to the processing of EBR-II SNF has been carried out on melt and dilute. No development schedule or cost estimates were presented; therefore the committee does not have sufficient information to evaluate melt and dilute as a viable alternative to EMT.

The development of a versatile head-end process to handle mechanical decladding, sodium removal, and zirconium sludge formation for EBR-II SNF for the Savannah River Site (SRS) PUREX facility does not seem justified for the purpose solely of treating the relatively small quantity of EBR-II fuel that will remain after the completion of the EMT demonstration.

As proposed, chloride volatility technology is applicable to a very limited range of fuel types. At present, considering also cost and schedule, the chloride volatility process concept is not competitive with the current EMT process. Earlier experimental work does not suggest to the committee that this approach is an attractive alternative to EMT.

Although plasma arc processing has been used successfully to treat nonradioactive and low-level radioactive wastes, significant research, development, and demonstration would be needed to process SNF because of the much higher fission product and fissile material content.

All of the processes evaluated, with the exception of the PUREX process, are at an early stage of development.

Although the PUREX process is well developed, the development of a versatile head-end process to handle mechanical decladding, sodium removal, and zirconium sludge formation for EBR-II SNF for the SRS PUREX facility would require a significant investment.

Although overpack does not require processing, direct emplacement of EBR-II SNF is presently precluded by DOE policy concerning acceptance of RCRA-designated mixed waste.

DOE furnished the following criteria for evaluating the success of the demonstration project. The committee's task was to evaluate these criteria to determine if they were adequate. The details of the criteria are developed more fully in the body of the report (Chapter 4).

Criterion 1: Demonstration that 125 EBR-II assemblies can be treated in a fuel-conditioning facility (FCF) within 3 years, with a throughput rate of 16 kg/month for driver assemblies sustained for a minimum of 3 months and a blanket throughput rate of 150 kg per month sustained for 1 month.

Criterion 2: Quantification (for both composition and mass) of recycle, waste, and product streams that demonstrate projected material balance with no significant deviations.

Criterion 3: Demonstration of an overall dependable and predictable process, considering uptime, repair and maintenance, and operability of linked process steps.

Criterion 4: Demonstration that safety risks, environmental impacts, and nuclear materials accountancy are quantified and acceptable within regulatory limits.

The ceramic and metal waste forms cannot be fully evaluated at the present time because acceptance criteria have not yet been established. The committee previously recommended that “DOE should establish acceptance criteria for waste forms scheduled for storage in a geologic repository. ”⁴ Similarly, the uranium product cannot yet be fully evaluated, because its ultimate disposition has not been decided. The committee believes that the overall goal of the demonstration is to show that the electrometallurgical process can be made to work at scale in a reasonable fashion; the goal at this stage is not to show that the waste forms will be satisfactory for geological disposal.

The committee finds that the criteria established by DOE are reasonable for judging the success of the EBR-II spent fuel treatment demonstration.

Confirmation that the waste forms produced by EMT are acceptable within the DOE's Office of Radioactive Waste (DOE-RW) Office of Civilian Radioactive Waste Management (OCRWM) program for final geological disposal must be a key component in a full qualification of the EMT process.

If DOE concludes that the EMT process is unsuitable for processing the remainder of the EBR-II fuel, then the PUREX process could be evaluated for its applicability to treatment of EBR-II spent fuel. However, a significant issue for treating EBR-II fuel at SRS by PUREX relates to public concerns about the transportation of the fuel from the current storage site at ANL-W to SRS.

In recognition of the progress that ANL has made in the demonstration and in accord with the committee's previous recommendations, the committee recommends to DOE that ANL's demonstration project be carried to completion.