An Assessment of Continued R & D into an Electrometallurgical Approach for Treating DOE Spent Nuclear Fuel (1995)

Satisfaction of this criterion is necessary to provide evidence that the process equipment, which can be serviced and repaired only with considerable difficulty and expense, is capable of operating continuously and with sufficient throughput for the multiyear period that will be required for completion of the EBR-II fuel-processing campaign. The 200 kg/day capacity corresponds to the specifications of the high-throughput electrorefiner that is now being developed.

• Quantification (for both composition and mass) of recycle, waste, and product streams thatdemonstrate projected material balance with no significant deviations.

  Satisfaction of this criterion would provide evidence that the proposed separations schemes, previously analyzed with synthetic spent fuels or by computational techniques, can reliably accomplish the required separations.

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

  Operating time can be limited by downtime associated with repair and maintenance, time to charge the process with feed materials and to remove the product(s), breakdown of upstream or downstream processes, and time required for retreating materials that do not meet the product specifications. Process utilization, defined as the ratio of operating time to calendar time, in the range of 70% would be acceptable from the standpoint of capital and operating costs, whereas a utilization of only 25% would call into doubt current assumptions about the capital costs and throughput capacity of a production plant.

• Demonstration that releases of radioactivity remain at or below those levels anticipated and specified in equipment design and operating plans. Exposure of operating personnel to radiation must be minimal and must in all cases remain below limits set by the U.S. Nuclear Regulatory Commission.

  Safety and contamination considerations make it essential that levels of exposure be accurately anticipated and that the resulting performance standards be met.

Specific elements of the ANL proposal are appropriate and necessary to support the EBR-II program, whereas other elements are intended for other purposes that are not essential to the EBR-II processing plan. The specific elements from ANL's proposed activities through the spring of 1996 that are necessary for the treatment of EBR-II fuel and blanket assemblies are the following:

• Conclude tests of anode screen basket for fission product recovery;

• Demonstrate high-throughput electrorefiner design concept;

• Demonstrate the full-scale cathode processor;

• Demonstrate electrolyte filtration for particulate removal;

• Demonstrate engineering-scale zeolite column, dehydrating, and hot blending preparation equipment;

• Establish parameters for a metal waste form melting furnace; and

• Demonstrate multistage pyrocontactor for removal of TRUs from electrolyte salt.

If the DOE decides to develop the electrometallurgical process as a possible treatment for N-reactor fuel from Hanford, the following steps from the ANL proposal through spring of 1996 will also be required:

• Complete dissolution tests with unirradiated N-reactor fuel;

• Test anode assembly concept for high throughput of N-reactor fuel;

• Obtain 20 to 30 N-reactor fuel assemblies at ANL-West;

• Develop process chemistry for oxide reduction and lithium recycle;

• Develop accurate mass-balance statistics; and

• Install pump/filtration equipment in the Fuel Conditioning Facility.

Because there are no current plans to apply the electrometallurgical process to Hanford's K-basin sludges, oxide fuels other than oxidized N-reactor assemblies, or waste forms, the committee believes that the portions of the ANL proposal relating to these important problems are premature.

Underlying all these processing activities is the clear but infrequently articulated need to provide absolute assurance that a critical mass cannot be accumulated during any process step. The size of specific hardware and equipment items, process flow sheets, and system configuration together with storage arrangements will be important to providing this assurance.

The committee believes that a geologic repository will not be ready to receive material for many years, and interim storage of at least 20 years will be unavoidable for end products and waste streams from any DOE fuel treatment process. If such processes were to yield separated uranium and plutonium, the storage problems would be significantly increased, as would the need to safeguard these separated materials from theft and diversion. Above all, product streams from this development program must be of a nature that their later treatment for ultimate disposal after interim storage is not precluded.

The progress of the electrometallurgical treatment program needs to be monitored by the DOE and assessed periodically to determine its continued technical viability and schedule and budget effects. As stated above, this involves oversight primarily of the EBR-II spent fuel treatment program and secondarily of the supporting ANL proposal items noted above.

The committee noted the following apparent advantages and disadvantages of the electrometallurgical technique as a candidate technology for treatment of DOE SNF.

• Small compact equipment should result in a relatively small facility.

• Recycle of principal process reagents should result in generation of a small volume of waste.

• Use of radiation-resistant reagents (e.g., CdCl₂ and LiCl/KCl) should reduce waste volumes.

• Effluent waste streams would be more uniform for different SNFs than would be the case for direct disposal of the different SNFs.

• The high process temperatures ensure that chemical kinetic factors will not be process limiting.

• A large body of basic and applied information on the process suggests its fundamental workability.

• It should be possible to generate a high-level waste form having a very low TRU content and having a heat-producing half-life of approximately 30 to 35 years. This form could open new options for waste management.

• The uranium product could be blended to reduce its enrichment.

• The electrometallurgical process will not readily handle all types of DOE SNF; head-end processes need to be developed.

• Waste forms are not yet developed, qualified, certified, or accepted.

• An inert atmosphere is required, with related operating and maintenance drawbacks.

• The process has not been proven or demonstrated to be operable remotely in a radiation environment.

• The equipment (pyrocontactors) for removal of uranium and TRUs from the electrorefiner waste salt is still in development.

• The overall program plan, laid out for 6 years into the future, does not appear to result in a plant or complete unit, but rather only a demonstration of the various components needed for a complete fuel processing facility.

• Uranium and TRU products might be considered waste, destined for TRU waste storage or permanent disposal. Disposal would probably require oxidation of the uranium metal and TRU metal streams to oxides. If the uranium product were to be a waste stream but not acceptable for geologic disposal, the additional processing steps (e.g., oxidation) would bring into question the usefulness of the proposed electrometallurgical technology.

• Demonstration of the process adds to the risk that a nation intent on weapons production might consider adapting this technology for possible production of (relatively poor) fissile material.

These advantages and disadvantages lead to the conclusion that electrometallurgical processing is technically appealing mainly for treatment of metallic SNF, of which N-reactor fuel constitutes the lion's share. Regarding justification for a commitment to the long-term expenditures necessary to maintain a viable basis of process expertise for possibly treating N-reactor fuel, the committee is concerned about (1) general limitations on the applicability of the electrometallurgical process, (2) schedule uncertainties and the delays likely to occur before the process could be used for treatment of SNF other than intact EBR-II fuel and blanket assemblies, and (3) unanswered questions about the electrometallurgical process products and waste forms. Of particular concern are the following:

• Plans are already being laid to stabilize and store the N-reactor fuel without the use of electrometallurgical processing,¹ and that activity might well be under way before the electrometallurgical technology has been fully demonstrated.

• The electrometallurgical technology is not immediately applicable to the breached N-reactor fuel, which would require specialized head-end processes, mechanical and chemical.

• The electrometallurgical technology would generate new waste forms. The fate of the cladding-metal waste form is a major open question, and qualifying the zeolite waste form for burial could present major challenges.

Notwithstanding the above disadvantages and concerns, it is desirable that the process technology base at ANL be kept viable as a problem-solving resource until the EBR-II fuel has been processed. Much of the technology has not been demonstrated, and the capability for solving unanticipated problems as they arise during EBR-II fuel processing is essential.

Given the uncertainties, which will not be resolved for several years, the committee makes the following overall recommendation:

ANL should proceed with its development plan in support of the EBR-II demonstration. Further development of the lithium reduction process should be carried out only if the DOE decides that it is likely that the electrometallurgical approach will be pursued as a possible treatment for the oxidized N-reactor fuel at Hanford. If the EBR-II demonstration is not accomplished successfully, the ANL program on electrometallurgical processing should be terminated. On the other hand, if the EBR-II demonstration is successful, the DOE should revisit the ANL program at that time in the context of a larger, “global” waste management plan to make a determination for possible continuance.