Neutronic investigation of prospective dual-cooled micro-heterogeneous duplex fuel for small modular long-life reactors: Assembly level design and analysis

Abstract

Nuclear fuel is a critical component of any nuclear reactor, influencing both its safety and economic viability. Continuous fuel quality improvements resulted in a significant reduction in failure rate, and assembly design changes contributed to a significant increase in power density and performance during irradiation. In terms of fuel development, a new fuel type called “dual-cooled annular fuel” has recently been proposed to be used in nuclear reactors. The dual-cooled annular fuel design benefits from heat transfer to the coolant at both the outer and inner channels. Another emerging trend in nuclear fuel development is the use of thorium-based fuel in the form of duplex fuel design. As a result, the current work is an attempt to incorporate potential dual-cooled annular duplex fuels into the assembly of an innovative Small Modular Reactor (SMR). This paper, therefore, compares the neutronic properties of annular duplex fuel to those of annular UO2 fuel. Considering the dual-cooled feature, this study presents both duplex configurations (i.e. ThO2– UO2 and UO2–ThO2). The neutronic properties include fissile loading determination, multiplication factors, discharge burnup, and isotopic concentration. This analysis also determined the reactivity coefficients, power peaking factors, energy-dependent neutron flux, and an analysis of possible burnable absorbers and configurations. The results of this study show that both annular duplex fuels can achieve 6% higher discharge burnup than annular UO2 fuel, despite nearly identical reactivity values at the beginning of the cycle. The production of plutonium and other minor actinides has been greatly reduced. Annular duplex fuels have lower power peaking factors, which are beneficial for reactor operation, and the UO2–ThO2 configuration performs better. The calculated reactivity feedback coefficients show negative patterns and are within the annular UO2 fuel's range. The proposed annular duplex fuel designs have additional intriguing neutronic properties that open up possibilities for future research.