Physical study of an ultra-long-life small modular fast reactor loaded with U-Pu-Zr fuel

•Physical study of an ultra-long-life small modular fast reactor with small burnup reactivity swing was performed.•Small burnup reactivity swing was achieved through the optimization of the U-Pu-Zr fuel composition.•The effect of decay of 241Pu on the burnup reactivity swing was identified.