In early 1995 the DOE set the following milestones for activities to address these concerns:6

  • Fuel removal from K-basins at Hanford to be completed by December 1999;

  • Fuel consolidation, processing of SNF and target assemblies, and stabilization of resultant uranium solutions at Savannah River by April 2000; and

  • Removal of all fuel from CPP-603 by December 2000.

In their present form and condition the EBR-II and N-reactor fuels are not suitable for direct geologic disposal, and even long-term interim storage would require repackaging or some other treatment. 7 The principal goal for treating these fuels would be to put them into a safe and stable condition for interim storage until their ultimate disposition can be decided. Because the proposed Yucca Mountain repository cannot be available until after 2010, at the earliest, to receive any spent fuel consigned to geologic disposal, there is an unavoidable need to attend to these two categories of fuel (about 80% by mass of the DOE's total spent fuel inventory), as well as other spent fuels not already suitable for storage, to permit their interim storage for an estimated 20 to 40 years prior to final disposition.

POSSIBLE CANDIDATE FUELS FOR ELECTROMETALLURGICAL PROCESSING

The electrometallurgical technology developed by ANL is potentially applicable to a fairly wide variety of spent fuel types. In principle, electrometallurgical separations in alkali metal chloride media could be used for most of the DOE SNF, if used in conjunction with appropriate head-end processes. The purpose of specially tailored head-end processes would be to convert the fuels to metal and free them from elements such as aluminum and carbon that, above certain threshold-level concentrations, are incompatible with the electrometallurgical process as currently conceived.

The DOE has already determined that the EBR-II driver fuel and at least half of the blanket fuel will be treated via the electrometallurgical process. It is expected that, in addition to processing EBR-II fuel, the electrometallurgical technology could process undamaged, metallic fuels from the Hanford N-reactor without any lithium-reduction head-end treatment. N-reactor fuels constitute about 80% by mass of DOE's SNF inventory and EBR-II fuels about 1%.

However, a significant fraction of the N-reactor fuel elements have experienced a breach in their cladding, and these failures have resulted in oxidation of the uranium metal as well as the zirconium cladding. These failed fuel elements (and the accompanying sludge that has formed in Hanford's K-basin East) would have to be treated by head-end processing such as chemical purification and oxide reduction

6  

“Defense Nuclear Facilities Safety Board Recommendation 94-1 Implementation Plan,” Department of Energy, Feb. 28, 1995.

7  

Uranium and zirconium metals are chemically reactive in water and in air, and powdered forms of these metals are pyrophoric. In the reaction with water, hydrogen is also produced, and under conditions of limited oxygen, uranium hydride may form as well. Initially, uranium dioxide forms a protective coating on the metal surface that greatly retards further oxidation, but after an indeterminate time, the protective layer cracks and crumbles, allowing further oxidation to occur. Fuel elements with breached cladding will oxidize after contact with water, and the resulting physical changes at the uranium surface can lead to additional cladding damage and release of radioactivity into the water.



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