Neutronic analysis of sodium-cooled fast reactor design with different fuel types using modified CANDLE shuffling strategy in a radial direction

Abstract

This study compares three fuel types using neutronic analysis for use in a sodium-cooled fast reactor (SFR) design with a modified CANDLE (Constant Axial shape of Neutron flux, nuclide densities, and power shape During Life of Energy production) radial shuffling strategy. SFR is one type of generation IV reactor that is currently under investigation for commercial implementation. In this study, the SFR design utilizes natural uranium as the fuel input. The designed reactor core has a two-dimensional cylindrical geometry for each fuel mixed oxide (MOX), uranium-plutonium nitride ([U-Pu]N), and uranium plutonium zirconium ([U-Pu]Zr). A radial shuffling strategy, using natural uranium as the fuel input, is applied to the SFR to manage the nuclear fuel burn-up process of the long-life reactor. This strategy is called the modified CANDLE burn-up scheme. The reactor core is divided into 10 regions with equal volume to represent the 10 years that the reactor operates without refueling. Initially, the first (innermost) region of the reactor core is filled with natural uranium fuel. The result of the burn-up from the first region is then shuffled into the second region. The third region is the result of the burn-up that is shuffled from the second region, and so on. This mechanism only requires natural uranium as the input for each 10-year fuel cycle. In this study, the fuel movement scheme is examined for three fuels. Global neutronic parameters, such as the multiplication factors and burn-up analyses, are observed and optimized. Overall, for an output power of 500 MWth and an active core radius of 110 cm and height of 210 cm, the study indicates that (U Pu)N is the optimal fuel to be applied in the SFR with a modified CANDLE burn-up scheme. (U-Pu)Zr reaches a critical condition at an output power of 500 MWth with an active core radius of 130 cm and a height of 210 cm; whereas criticality for MOX is achieved at an output power of 1500 MWth with an active core radius of 210 cm and a height of 210 cm.