Small modular reactor core design for civil marine propulsion using micro-heterogeneous duplex fuel. Part I: Assembly-level analysis

•Advanced SMR assembly has been designed for marine propulsion core.•Thorium-based micro-heterogeneous duplex fuel has been used.•SMR assembly is designed for soluble-boron-free and long life core.•Assembly-level behaviours of reactivity control schemes are investigated.•Underlying physics of soluble-boron-free assembly has been investigated. In an effort to de-carbonise commercial freight shipping, there is growing interest in the possibility of using nuclear propulsion systems. In this reactor physics study, we seek to design a soluble-boron-free (SBF) and low-enriched uranium (LEU) (