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

Location: Argonne National Laboratory (ANL)-West Facility, Idaho National Engineering and Environmental Laboratory

Attendance: G. Choppin (chair), M. Apted, P. Baisden, S. Burstein, E. Flanigan, E. McNeese, R. Osteryoung, D. Raber, M. Seitz, J. Sherman.

Unable to attend: J. Aherne, J. Williams, R. Wymer.

Augmented by guests John P. Ackerman (ANL), Robert W. Benedict (ANL), Yuon I. Chang (ANL), Dan Funk (DOE), Eddie C. Gay (ANL), K. Michael Goff (ANL), Stephen G. Johnson (ANL), Dennis D. Keiser, Jr. (ANL), James J. Laidler (ANL), Shelly X. Li, Sean McDeavitt (ANL), and Denis M. Strachan (ANL).

Gregory R. Choppin convened the meeting at 8:15 a.m. in the L & O Conference Room, ANL-W.

Yuon Chang, ANL-West, discussed the budget deliberations leading to the current budget of $20 million for fiscal year 1998. Mr. Charles Till will be retiring in December 1997, at which time Chang will sit in as associate Laboratory Director. Day to day operations of the Electrometallurgical Technology (EMT) program will be handled by Bob Benedict. At the top level, the EMT has four criteria to meet. The presentation today concerns the second-level goals that address the four criteria.

Robert W. Benedict, ANL-West, outlined the spent fuel treatment demonstration project. Within the project, ANL plans and executes the demonstration for treating a portion of the Experimental Breeder Reactor (EBR)-II fuel that is held on site, integrates program activities at ANL-W and ANL-E, and provides in-cell process equipment for the demonstration phase and subsequent treatment of ANL-W spent fuel inventory. The four criteria of the program are (1) the demonstration that 125 EBR-II assemblies can be treated in the Fuel Conditioning Facility (FCF) within 3 years; (2) the quantification of recycle, waste, and product streams; (3) demonstration of an overall dependable and predictable process; and (4) demonstration that safety risks, environmental impacts, and nuclear materials accountancy are quantified and acceptable.

John P. Ackerman, ANL-E, described the waste handling in pyroprocessing. The metal waste has excellent durability and mechanical properties and has a composition that is unchanged from that specified last year. Glass-bonded sodalite has been selected as the ceramic waste (over glass-bonded zeolite) because of its anticipated durability and excellent retention of radionuclides. Also, sodalite is favored because of its insensitivity to processing variables. Cold compact and pressureless sintering of the ceramic waste appears feasible and would avoid many of the complications of hot isostatic pressing. ANL completed work on the pyrocontactor and will write the final report.

K. Michael Goff, ANL-W, addressed the qualification of the reference ceramic waste. Hot isostatic pressing (HIP) could produce a product with fewer cracks by using the bellows can developed by the Australian Nuclear Science and Technology Organization. ANL has reached a final cooperative research and development agreement to use this technology. Goff described the plan to obtain the HIP cans of sodium-bonded sodalite for testing. The cans will contain the transuranic elements and fission products

from processing the EBR-II fuel. The program has developed leak-tight containers to handle the zeolite containing less than 0.1 percent water.

Stephen G. Johnson, ANL-W, directed attention toward measures to define the quality of the waste products. A battery of tests will define the acceptable envelope for operational functions and materials processing parameters. Examples of tests are electron microscopy and x-ray spectroscopy to reveal microstructure and the location of radionuclides.

Denis M. Strachan, ANL-E, continued the discussion of waste form qualification by describing the hydration and leach tests to which the waste forms would be subjected. The demonstration program will use the experience of certifying wastes from the Defense Waste Processing Facility and the West Valley Plant. So the ANL qualification program will develop documents on waste form acceptance, product specifications, compliance plans, and the qualification report. The DOE responsible organization will write the waste form acceptance document with review and concurrence by the HLW program. ANL will develop the compliance plan that includes the product specifications and will publish the qualification report that presents the test data.

Sean McDeavitt, ANL-W, characterized the metal waste form by metallurgical description of the iron solution metal phase, the intermetallic, Zr(Fe, Cr, Ni) _2+x, phase, and the small-volume (<10 percent) Zr₆Fe₂₃-type phase. Qualification tests of the metal waste form include accelerated tests, service condition tests, mechanical testing, and thermophysical properties measurements.

Dennis D. Kaiser, Jr., ANL-W, focused on the production of the metal waste forms that would be tested as part of the treatment demonstration. The production starts with the characterization of irradiated cladding hulls and concludes with the casting of the metal waste ingots. Incomplete melting of the zirconium hulls is caused by heat loss from the high-temperature furnace. Also, the addition of nonirradiated zirconium and stainless steel seems to help initiate melting. Characterization of the irradiated cladding hulls is complete. The furnace will be modified to generate mid-sized metal waste ingots.

Stephen G. Johnson, ANL-W, addressed the committee again, this time on the metal waste form testing program. Samples for the test program bracketed the compositions expected from the treatment demonstration. In order to simulate a worst case scenario, metals containing technetium were leached in deionized water heated to 90 ºC. Leached technitium was determined using liquid scintillation. Measured reaction rates were used with reasonable assumptions to extrapolate that a thickness of 80 × 10⁻⁶meters or 3 thousandths of an inch would be reacted in 1,000 years under these extreme corrosion conditions. This was a scoping calculation, with very rapid rates of decomposition initially, mostly in the first month. This rate is not expected over time, certainly not under standard temperature and moisture.

Shelly X. Li, ANL-W, focused on the electrorefiner by discussing throughput as a function of the geometry of the anodes and cathodes, and the current and voltage histories during refiner operation. Preparations for the high-throughput modifications to the Mark-IV and the newly designed Mark-V refiners are being coordinated between ANL-W and ANL-E. It is difficult to separate uranium and zirconium even though their electrochemical potentials differ by 0.4 volts. From June 1996 through October 1997, 144 kilograms of spent fuel have been processed. ANL-E is producing UCl₃ that will be used as an oxidant that is introduced into the ER.

Eddie C. Gay, ANL-E, designs the electrodes for the HTER. The HTER is a refiner operated at ANL-E to support design of the Mark-V refiner. Gay specified the features needed for high throughput including

scrapers to remove refined uranium during a complete run. The electrical charge (measured in ampere hours) needed to electrorefine a kilogram of uranium is a measure of the refiner potential. Also, the HTER has been used to produce UCl³ needed for the Mark-V processing. Tests using the HTER and UCl³ production are on schedule to support the EMT demonstration.

James J. Laidler, ANL-E, described the EMT in light of other spent fuels DOE would need to process for disposition. Sodium-bonded fuels such as EBR-II, Fermi-I, and Fast Flux Test Facility fuels, can be treated directly. Oxide fuels would require reduction, such as that produced by lithium metal. Reduction rates are accelerated to useful rates using porous lithium cathodes that are produced in the reduction of lithium. Also, EMT had been identified as a backup approach to treating aluminum-clad fuels, although direct disposal and treating problem fuel in existing process canyons were identified as the preferred approaches. To process aluminum-clad fuel, EMT would first separate aluminum as a LLW after the addition of silicon to bind the uranium. Then uranium would be extracted. For aluminum-clad U³O⁸ fuel, the uranium oxide would have to be reduced before subjecting the fuel-salt mixture to EMT.

Dan Funk, representing the Office of Nuclear Energy, Science and Technology (NE) of the Department of Energy, discussed NE's interest that NE has in an objective evaluation of EMT for EBR-II fuel. The office would appreciate input from the committee on alternatives to EMT for EBR-II fuel and on the potential for applying EMT to some of DOE's other fuels. Mr. Funk described that the NE office will be developing an environmental impact statement for the treatment of spent fuel and has the responsibility to consider all reasonable alternatives.

The open discussion included clarification that some of the testing of waste forms will be under way but still incomplete at the end of the demonstration project. Also, Japan's and England's interest in EMT, as alternatives to aqueous processing, were discussed in light of the EMT demonstration project.

The committee met from 7:30 a.m. to 12:00 noon at conference facilities within the Shilo Inn, Idaho Falls, ID. The chairman followed the agenda as published above. The chairman issued research and writing assignments and scheduled two meetings of the committee, one for February 5 and 6, the other for March 16 and 17, 1978. Both meetings will be at the National Academy of Science facility in Washington, D.C. Following these meetings, the committee is expected to publish a report on its findings.