The Mk1 PB-FHR is designed so that all components—including the reactor vessel, gas turbine, and building structural sub-modules—can be transported by rail, enabling modular construction. FHRs can be designed to implement passive safety even at gigawatt power levels; however it is a pragmatic choice for the Mk1 design to select a lower power level for the first commercial FHRs, comparable to the typical light-water small modular reactors (LWR-SMRs) now under development.