Conceptual Neutronic Design of a Lead-Bismuth-Cooled Actinide Burning Reactor

A conceptual design of a lead-bismuth-eutectic (LBE)–cooled actinide burner core with innovative streaming fuel assemblies (FAs) is described. The 1800-MW(thermal) core employs metallic, fertile-free fuel where the transuranics (plutonium plus minor actinides) are dispersed in a zirconium matrix. The core contains 157 streaming FAs that enhance neutron streaming by employing gas-filled, sealed streaming tubes at the FA periphery and center. The large reactivity excess at the beginning of life is compensated for by a system of double-entry control rods. The arrangement of top-entry and bottom-entry control rods in a staggered pattern allows the achievement of a very uniform axial power profile and a small reactivity change from control rod driveline expansion. The reactor can operate with an 18- to 24-month cycle length.Safety is provided through negative reactivity coefficients and tight neutronic coupling. The void coefficient is negative for a partially as well as a fully voided core. The effective delayed neutron fraction is 25% less than that of typical oxide-fueled fast reactors, making the requirements on reactor control performance more demanding. The Doppler coefficient is negative with a magnitude appreciably lower than the typical values of oxide fuels in sodium-cooled reactors, but comparable to the values observed in integral fast reactor (IFR) cores with metallic U-Pu-Zr fuels. The fuel thermal expansion coefficient is also negative, having a magnitude approximately equal to the Doppler coefficient. In terms of the transuranic destruction rate per MW(thermal) per effective full-power year, the design is comparable to accelerator-driven systems (ADSs). Long-lived fission products also can be transmuted, albeit at lower incineration efficiency than in ADSs.