A neutronic design study of lead-bismuth-cooled small and safe ultra-long-life cores

In this paper, two small ultra-long-life lead-bismuth-cooled cores having 48 and 58 effective full power years (EFPYs) of operation life are neutronically designed, and their core physics characteristics including safety-related parameters are analyzed and inter-compared. Each core's rate is 110 MWt (36 MWe), and they use depleted uranium and thorium blankets, respectively, for achieving ultra-long life and high burnup while the ternary metallic fuels having TRU from LWR spent fuels are adopted as driver fuels. They adopt a low power density for ultra-long life and for considering some possibilities of high peak power density. This work provides a consistent comparison of the effects of the depleted uranium and thorium blankets on the performances of small ultra-long-life lead-bismuth-cooled cores. The results of the detailed neutronic analyses show that the core with depleted uranium has a significantly longer life because of the better breeding characteristics of depleted uranium versus the core with a thorium blanket and that all of the cores have negative reactivity coefficients except for the very small positive coolant expansion reactivity coefficients and low peak linear power densities. Additionally, a detailed decomposition analysis is performed to better understand the effects of coolant voiding on reactivity.