Comparison of Advanced-Technology-Fuel options in soluble boron-free Small Modular Reactors

Water-cooled Small Modular Reactors (SMRs) have gained significant attention as they could be modularised, standardised, and factory-fabricated to reduce capital cost and improve passive safety. However, SMRs often come with lower power density, which makes them less competitive with commercial LWRs. To enhance SMRs’ operation margin, deployment of the Advanced Technology Fuels (ATFs) can be beneficial. Therefore, this study examines the application of short-term ATF solutions in a soluble boron-free (SBF) SMR design inspired by Rolls Royce’s SMR. The analysis integrates neutronic and thermo-mechanical performance evaluations by means of advanced nuclear modelling tools: WIMS, PANTHER, and TRANSURANUS. The study focuses on core design parameters, including reactivity control, power distribution, shutdown margin and other design limits. In addition, fuel performance was investigated in terms of fission gas release (FGR), fuel temperature and cladding strain. The neutronic analyses suggest that the maximum peaking factors of SBF cores are about 15% higher than those of soluble boron-controlled cores. The deployment of FeCrAl cladding, Cr coating of conventional Zricaloy cladding and Cr doping of UO 2 fuel have a minor impact on both total power peaking and axial offset. On the other hand, the thermo-mechanical results show that Cr-doped fuel and Cr-coated cladding significantly improve fuel performance, reducing FGR and fuel temperature, while FeCrAl cladding offers limited benefits under the evaluated conditions. Comparative analyses indicate that SBF cores, while operationally viable, present unique design challenges due to a higher power peaking and associated thermal fluctuations, necessitating optimisation of control rod strategies and fuel assembly design. The findings demonstrate the feasibility of incorporating ATFs in SBF SMRs, aligning with European green taxonomy criteria for sustainable nuclear development. This study highlights the potential of combined Cr-doped fuel and Cr-coated cladding as a promising strategy to enhance performance in advanced nuclear reactor designs. • Feasibility: Boron-free SMRs show higher power peaking compared to boron cores. • Optimisation: Control rod movements cause power offset swings. • Fuel: A combination of Cr-doped UO 2 fuel with Cr-coated cladding improves performance. • Performance: ATFs in boron-free SMRs yield key benefits aligning with EU green standards.