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

be treated in a head-end operation to convert the fuel materials to metals or oxides, which can then be processed as above.

The key element of the electrometallurgical treatment method is the electrorefining step, where the actinide elements are separated from the fission products present in the spent fuel. The process is the same as the electrorefining process used for many years in the minerals industry: an impure metal is made the anode, and it is deposited at a cathode in a condition of greater purity by electrotransport through a suitable electrolyte. In the electrorefiner, virtually pure uranium is collected at a solid steel cathode and a mixture of plutonium, americium, neptunium, curium, uranium, and some rare earth fission products is collected at a liquid cadmium cathode suspended in the electrolyte salt. The noble metal fission products and the cladding hulls remain in the electrorefiner anodic dissolution baskets. The alkaline earth and alkali metal fission products remain in the electrolyte salt, from which they are later extracted.

The cathode deposits are recovered after the desired amount of material has been collected and are then sent to a cathode processor, which is basically a high-temperature vacuum furnace. The deposits are consolidated in the cathode processor by melting; in the process, any volatile materials that were included in the cathode deposits are removed by vaporization. These include the electrolyte salt in the case of the solid cathode uranium deposits, and cadmium in the case of the liquid cathode deposits. The distillates from the process crucible are transported to the condenser region of the cathode processor, where they are collected for recycle to the electrorefiner. The metal ingots resulting from the cathode processing operation are then placed in appropriate storage containers for interim storage pending a decision on final disposal. All of these operations are performed remotely, in a highly shielded hot cell facility, because the decontamination factor for fission products in the transuranic product is inherently low. Low decontamination provides self-protection and affords a high degree of diversion resistance to the nuclear materials contained therein.

The electrometallurgical method produces a convenient separation of the fission products present in spent fuel from the actinide elements. Pure uranium is separated from the transuranic elements and can be recovered for interim storage until its ultimate disposition can be decided. Similarly, the transuranic elements can be recovered and placed in a form suitable for interim storage, also pending a decision on the appropriate disposition of such materials. The fission products are recovered separately and immobilized in stable high-level waste forms, one metal and the other mineral, for ultimate repository disposal.

There are a number of incentives for the electrometallurgical treatment of the DOE spent fuels. Foremost is the production of a waste form of uniform composition, regardless of fuel type treated, that contains the active metal fission products (Cs, Sr, Ba, Br, I, Te, etc.). This waste form can probably be qualified for repository acceptance under the existing composition envelope for standard borosilicate glass. Further, the process of qualifying a large number of fuel types for repository disposal, which would probably be necessary for those fuel types differing substantially from zirconium alloy-clad low-enrichment oxide fuel (i.e., commercial light water reactor spent fuel), can be prohibitively expensive, and the electrometallurgical treatment would serve to homogenize a broad variety of wastes into a single, readily acceptable disposal form. A second significant incentive is the removal of fissile (highly-enriched uranium as well as transuranic elements) materials from the waste products; this would serve to dispel any concerns about the likelihood of an in situ criticality event, either in dry storage or after permanent

repository emplacement of these materials. The removal of the actinide elements from the waste means that only the fission products must be disposed in a repository, thereby gaining a reduction in waste volume. A third incentive for electrometallurgical treatment is the use of a low-cost, broadly-applicable method that can be implemented at each site storing significant quantities of spent fuel. By using a common approach at each site, and utilizing existing facilities to the greatest extent practical, the costs for disposing of the vast majority of the DOE spent fuel inventory can be minimized.

Argonne National Laboratory proposes to complete the development of the electrometallurgical treatment technology for application to selected DOE spent nuclear fuel types. The proposed program is directed toward a timely demonstration of the feasibility of application of the electrometallurgical treatment technology to the treatment of DOE spent fuels. Priority will be given to those fuels amenable to electrometallurgical treatment that (1) are chemically reactive or physically unstable and hence unsuited for direct repository disposal, or (2) are in a form that would make qualification for repository disposal prohibitively expensive. Examples of the former are metallic fuels and hydride fuels. Included in this group is the fuel from the Hanford N-Reactor (2,100 MTHM) and single-pass reactors (3.4 MTHM), from Fermi-1 (38.1 MTHM), and from EBR-II (48.4 MTHM). The second high-priority group is made up of FFTF mixed oxide fuel and failed fuel from the TMI-2 reactor and from test reactors such as PBF and LOFT. The TMI-2 core rubble, as an illustration, is packaged in 342 canisters bearing material of disparate composition; qualification of this material for disposal in a licensed repository would be a costly proposition. Emphasis will also be placed on development of a compatible electrometallurgical technique for treatment of Hanford storage basin sludge, so that the processing of Hanford storage canisters can be comprehensive.

Experimental facilities for carrying out the process chemistry development necessary to prove the feasibility of DOE spent fuel treatment are in place at the Argonne-Illinois site. Nearly-completed large-scale demonstrations of oxide fuel treatment will provide the basic information needed pertinent to DOE oxide fuels, and existing facilities can be used for confirmation of process chemistry for treatment of metallic fuels, hydride fuels, and other DOE spent fuel types. The Fuel Cycle Facility (FCF) at the Argonne-Idaho site will be available for demonstration of the treatment of actual DOE spent fuel types. Once that demonstration has been completed, a basis will exist for a decision to implement an electrometallurgical treatment capability at each of the DOE sites presently storing spent fuel, for on-site treatment of the particular fuel types in storage at a scale adequate to complete preparation for geological disposal in a reasonable period of time.

The proposed program is directed toward development of the electrometallurgical technology for treatment of “at risk” DOE spent nuclear fuels and demonstration of this technology at a scale that will provide a reasonable basis for a decision on the path forward for treating the appropriate fuels in the DOE spent fuel inventory. The program is organized into five major task areas: (1) Treatment of Metallic Spent Fuels; (2) Recovery and Treatment of Canister and Storage Basin Sludge; (3) Treatment of Oxide Spent Fuels; (4) Waste Treatment Processes; and (5) Waste Form Production and Qualification.

Treatment of Metallic Spent Fuels. This task is directed toward the electrometallurgical treatment of spent nuclear fuel from N-Reactor and the Hanford single-pass reactors. The ongoing EBR

II termination program, under which the EBR-II driver fuel and blanket assemblies are to be electrometallurgically treated for disposal, will provide a thorough demonstration of the process for treatment of Fermi-1 driver fuel and blankets, which are comparable to the EBR-II counterparts in terms of enrichment, cladding material, and use of bond sodium. The approach will be to demonstrate application of electrometallurgical treatment to low-enriched zircaloy-clad or aluminum-clad metallic uranium fuels, first with unirradiated fuels and then on a limited scale with irradiated fuels in the Fuel Cycle Facility. Established electrometallurgical flowsheets will be tailored to provide an efficient process for treating these spent fuel types, with initial emphasis on developing and demonstrating a process for rapid electrolytic dissolution of fuel materials from intact or damaged fuel elements. Development of a high-throughput electrorefiner concept, now well advanced, will be completed to provide the means for eventual production-scale treatment of this spent fuel type. The method now used for collection the pure uranium cathode deposit will be adapted to include means for cathode deposit processing to ensure high-rate production of a final U product that is free of fission products and transuranic element contamination. Recovery of a transuranic product for interim storage will be accomplished with a conventional liquid cathode. Major milestones for the FY1995-FY1997 period are as follows:

1. Complete dissolution tests with unirradiated segmented N-Reactor fuel elements (12/94) [COMPLETED]

2. Demonstrate high-throughput electrorefiner design concepts (3/95)

3. Demonstrate single-pass reactor fuel decladding process concepts (5/95)

4. Complete feasibility test of anode screen basket for fission product recovery (5/95)

5. Test anode assembly concept for high-throughput treatment of N-Reactor fuel elements (6/95)

6. Arrange shipment of 20-30 irradiated N-Reactor fuel elements to ANL-W (7/95)

7. Test cathode product compactor concept for purification of uranium and increase in throughput rate (9/95)

1. Complete design of SPR spent fuel decladding process equipment (4/96)

2. Complete demonstration of solid cathode product decontamination system for production of pure uranium (4/96)

3. Modify engineering-scale electrorefiner for high-throughput anode/cathode demonstration (6/96)

4. Complete test of equipment system for high-rate loading/unloading of electrorefiner anode baskets (7/96)

5. Complete engineering-scale demonstration of Single-Pass Reactor spent fuel decladding operations (8/96)

6. Complete hot demonstration (150 kg) of N-Reactor spent fuel treatment using the Fuel Cycle Facility Mk-IV electrorefiner (9/96)

1. Complete demonstration testing of electrorefiner cathode product compactor (2/97)

2. Complete fabrication of electrodes for electrochemical treatment of N-Reactor spent fuel in the Fuel Cycle Facility high-throughput (Mk-V) electrorefiner (2/97)

3. Complete plant-scale tests of high-throughput anode/cathode components (5/97)

4. Modify and test high-speed loading and unloading machine for anode baskets (7/97)

5. Complete tests of head-end fuel preparation concepts for breakdown of fuel elements for anode basket loading (9/97)

6. Initiate demonstration of high-speed electrorefining of irradiated N-Reactor fuel (9/97)

Recovery and Treatment of Canister and Storage Basin Sludge. Because the unopened N-Reactor fuel storage canisters in the K-West storage basin are thought to contain sludge bearing significant quantities of fuel and fission products, and because there are copious amounts of contaminated sludge at the bottom of the K-East storage basin, the treatment of N-Reactor fuel is incomplete without dealing with the contaminated sludges. This task is intended to provide the means for recovering those sludges and introducing them into the same electrometallurgical treatment process as the fuel elements, to preclude the need for development of a separate sludge treatment process. The work will involve the adaptation of an existing centrifugal product collection system for use with the variable-density sludge that must be recovered. Initial development work will be carried out with simulated sludge materials and will include a demonstration of the reduction of the sludge for separation of inert materials, fission products, and actinide elements. Prototype equipment will be fabricated and tested in a basin mockup and prepared for use in recovery operations at Hanford. Collected sludge samples will be treated in the Fuel Cycle Facility or the Hot Fuel Examination Facility to provide a hot demonstration of the process. Major milestones for the FY1995-FY1997 period are as follows:

1. Produce sludge simulant based upon chemical and physical analysis of KE-basin sludge (2/95)

2. Fabricate sludge collection baskets for use in centrifugal collector (2/95)

3. Complete evaluation of variables affecting sludge recovery and compaction in collection tests with simulated sludge (7/95)

4. Conduct 1-kg scale reduction experiments with simulated sludge (9/95)

1. Complete analysis of reduction experiments with simulated sludge (12/95)

2. Demonstrate sludge collection design concept with removable containers for storage/shipment (3/96)

3. Complete design of collection device for hot demonstration at K-basins (5/96)

4. Complete fabrication of sludge processing system for Hanford demonstration (9/96)

1. Initiate sludge removal demonstration operations at Hanford K-basins (11/96)

2. Package and ship collected sludge to Fuel Cycle Facility (1/97)

3. Complete reduction of collected sludge (5/97)

4. Complete production of waste forms from sludge and initiate performance testing (9/97)

Treatment of Oxide Spent Fuels. The electrometallurgical treatment of intact oxide fuels, as typified by the FFTF spent fuel, involves a straightforward lithium reduction step that will be demonstrated initially with simulated fuel and subsequently with a limited number of irradiated fuel elements. This process can be applied to any of the numerous lots of oxide fuel in the DOE inventory. The electrometallurgical technique for treatment of TMI-2 rubble, which consists of a complex mixture of fuel and control materials, cladding, and assembly structural components, will begin with conversion of the hydrides and metallic materials to the oxide form. This will be followed by reduction with lithium metal and electrorefining of the metallic reduction product to separate the uranium, fission products and transuranics. Confirmation of the process chemistry for the conversion step will be required, and will be done initially with a simulated fuel mixture. Development of a comminution process for breaking up the rubble into pieces that will allow access of process reagents will also be necessary. Following successful demonstration of the process flowsheet with simulated FFTF fuel and TMI-2 rubble, a hot demonstration of the process will be carried out in the hot cells at ANL-West to provide assurance of process feasibility, including all aspects of the process from rubble comminution to waste form production. The treatment of oxide spent fuel from the Power Burst Facility (PBF) and Loss-Of-Flow-Test (LOFT) reactors will follow the same path as the FFTF oxide fuel. Development requirements are limited to establishment of a simple process for dismantlement of the fuel assemblies. These fuels can be treated in their entirety as part of the hot demonstration of the oxide fuel treatment process in the FCF. Major milestones for the FY1995-FY1997 period are as follows:

1. Develop process chemistry for dehydriding and oxide reduction steps (3/95)

2. Develop mass-balance flowsheet for oxide fuels (5/95)

3. Complete demonstration of reduction of simulated FFTF/LWR oxide spent fuel (5/95)

4. Compile data on characteristics of TMI-2 rubble in storage at INEL (6/95)

5. Establish flowsheet for TMI-2 rubble (9/95)

1. Prepare simulated TMI-2 rubble for process demonstration (11/95)

2. Develop process flowsheet and equipment for treating U-Zr hydride fuels (12/95)

3. Install oxide reduction vessel in ANL-W hot cell (5/96)

4. Demonstrate treatment of TMI-2 rubble with simulated fuel material (6/96)

5. Confirm process flowsheet for treatment of PBF and LOFT spent/damaged fuels (7/96)

1. Ship TMI-2 canisters to Fuel Cycle Facility for hot demonstration (11/96)

2. Complete reduction demonstration with FFTF fuel and TMI-2 rubble (6/97)

3. Start production of waste forms from FFTF fuel and TMI-2 rubble treatment (9/97)

4. Ship LOFT/PBF spent/damaged fuel to Fuel Cycle Facility for treatment (9/97)

Waste Treatment Processes. Waste treatment processes have been established through laboratory-scale testing, and it is now necessary to develop the processes at the engineering scale. The principal items of waste treatment equipment requiring scaleup are the multi-stage pyrocontactor for

removal of residual transuranic elements from the spent electrolyte salt, the zeolite column and associated equipment for extraction of fission products and their immobilization, and hot-pressing equipment for consolidation of the waste-bearing zeolites into solid monolithic form. Major milestones for the FY1995-FY1997 period are as follows:

1. Install and demonstrate engineering-scale zeolite column equipment (3/95)

2. Complete demonstration of electrolyte filtration for removal of particulates (3/95)

3. Begin demonstration of multi-stage pyrocontactor system for removal of residual transuranic elements from electrolyte salt (3/95)

4. Establish metal waste form melting furnace operating parameters (4/95)

5. Verify zeolite surface salt removal process (6/95)

6. Demonstrate zeolite preparation equipment: dehydrating, hot blending (8/95)

7. Demonstrate mineral waste form consolidation process (9/95)

1. Install pump/filtration system in the ANL-W Fuel Cycle Facility (4/96)

2. Complete design of multi-stage pyrocontactor for use in the Fuel Cycle Facility (5/96)

3. Complete modifications to the Fuel Cycle Facility casting furnace for metal waste form production (7/96)

4. Install mineral waste form consolidation equipment in the ANL-W hot cells (7/96)

5. Complete design of zeolite absorption column and ancillary equipment for installation in the Fuel Cycle Facility (9/96)

1. Conduct demonstration testing with hot multi-stage pyrocontactor (1/97)

2. Initiate conceptual designs of waste treatment and waste form production equipment for on-site treatment of metallic spent fuels, oxide spent fuels and storage basin sludge (1/97)

3. Conduct demonstration testing of zeolite absorption column with hot waste streams at ANL-W (9/97)

Waste Form Production and Qualification. Mineral waste form development activities will focus on the verification of the chemistry and physical performance of both pure and clay-bonded zeolite-based waste forms. A selection of the final candidate waste form, between a glass-bonded zeolite and sodalite, will be made after completion of screening tests. Testing of a zeolite column system will be carried out to verify the kinetics of fission product adsorption, leading to a cold demonstration of the waste form production process at the 1 kg batch size. A hot demonstration of the production of the mineral waste form will be conducted as soon as sufficient waste material is available from demonstration of the electrometallurgical treatment processes. An evaluation of the feasibility of including the transuranic elements in the mineral waste form will be done at the laboratory scale. Formulation of the metal waste form, which includes the cladding materials and the transuranic elements, will be developed for the range of spent fuel compositions under investigation. Scaleup from