DOE OSTI2016
Metallic fuels have a history of use that spans the entire nuclear age, especially in association with the development of the LMFBR. Initially, metallic fuels were employed due to their ease of fabrication and high heavy metal density (which led to the most favorable breeding efficiencies in fast reactors). During subsequent decades of use, metallic fuel technology has matured significantly, leading to the realization of major benefits in the areas of fuel reliability and burnup, proliferation-resistant recycling, remote fabrication, and passive reactor safety. Such characteristics continue to make metallic fuels a highly attractive technology, especially for use with future sodium fast reactors. Current research and development activities on metallic fuels in DOE's Advanced Fuels Campaign are focused on their potential use for actinide transmutation in advanced SFRs. In such a mission, metallic fuels would be employed as part of a closed fuel cycle into which plutonium and minor actinides (Am, Np) recovered from LWR spent fuel would be incorporated. All actinides in this metallic fuel would be fissioned or transmuted in a fast reactor to eliminate the extremely long-lived, heat-producing actinides in order to reduce the volume, heat load, and radio-toxicity burden on a future geological repository. Thus, the need exists to demonstrate reliable performance of metallic fuels with Pu and minor actinide constituents to very high burnup. As part of this application, there is also a need for a near zero-loss fabrication process, since losses during fuel fabrication are a potential source of long-lived actinides destined for geologic disposal. This paper presents the current state and future direction of the development of metallic fuels for actinide transmutation in the US. Metallic fuels have had a long history of use in sodium-cooled fast reactors. Continued research, development, and design innovation over a period of decades have demonstrated this fuel technology to be safe and reliable to extremely high burnups over a wide range of compositions. Their simple fabrication has historically given them a significant economic advantage over other fuel forms. Research and development on metallic fuels continues, with particular emphasis on showing that this fuel technology can incorporate significant quantities of plutonium and minor actinides for the purpose of efficiently and economically transmuting these elements in a fast-spectrum reactor. New fabrication methods to improve retention of the volatile fuel constituents during the casting process (and reduce waste generation), are being developed. Irradiation testing of the new metallic fuels has so far indicated that the new compositions, although differing significantly both in the quantities of Pu and minor actinides included and in the Zr alloying addition, perform as a function of fission density very analogously to the historic U-Zr and U-Pu-Zr fuels. In the next few years it is anticipated that a new casting furnace prototype will demonstrate that these new metallic fuel alloys can be fabricated at engineering scale, in a remote environment, with no significant fuel loss or waste generation. Irradiation tests currently underway will provide the performance data needed to assess fuel reliability/burnup capability and identify any unique behaviors that are a result of the new compositions. If these future results are consistent with the intermediate data available at present, metallic fuels are expected to continue to be a strong contender for the fuel technology choice of future fast reactors. (authors)
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗