Design Strategies for Lead-Alloy-Cooled Reactors for Actinide Burning and Low-Cost Electricity Production

A multi-year project at the INEEL and MIT is investigating the potential of lead or lead-bismuth (lead-alloy) cooled fast critical reactors for producing low-cost electricity as well as for burning actinides from LWR spent fuel. While these two goals are the primary thrust in the development of a conceptual design, the proliferation resistance of the fuel and the plant safety are also important constraints incorporated into the design process. Thus, this concept addresses all Generation IV reactor goals, which involve favorable economics, enhanced safety, and sustainability. This paper outlines the objectives of the project, the challenges shaping the design strategy, and the approaches adopted to achieve the design goals. The most promising path forward is also identified. The four key factors that influence the direction of the design and also require compromise are the actinide destruction rate, safety, economy, and proliferation resistance. Achieving a maximum actinide destruction rate per MWth requires fertile-free fuels. However, the achievement of safe reactivity coefficients in such cores is difficult. If the total elimination of actinides from LWR spent fuel is pursued, multiple reprocessing with high recovery efficiency is necessary. This will probably significantly increase the fuel cycle costs, thus negatively affecting the economics. On the other hand, in-situ breeding and burning of plutonium in cores initially loaded with U235 can be cost effective. However, such a system does not achieve any reduction in the actinide inventory, and the discharge fuel contains relatively pure Pu239, which poses a potential proliferation threat. To reconcile these competing goals, a number of approaches have been investigated to achieve a balanced design that is cost competitive with other alternatives for electricity generation, attains excellent safety, helps in the reduction of transuranics from the spent LWR fuel, and has discharged fuel that is at least as proliferation resistant as spent LWR fuel from a once-through cycle. The preliminary design of the reactor concept that has the best potential to achieve these characteristics is identified and briefly described. This concept incorporates a supercritical carbon dioxide power conversion cycle that achieves thermal efficiencies up to 45% at a core outlet temperature of 550°C. However, conventional steam cycles are also an option.