US swaps nuclear rods for control drums to advance next-gen reactors

Engineers at Idaho National Laboratory (INL) have achieved a significant advancement in the development of the MARVEL microreactor by successfully assembling and testing a novel Reactivity Control System (RCS) that replaces traditional vertical nuclear control rods with high-precision rotating control drums. Unlike bulky control rods that require vertical space, these compact drums rotate around the reactor core’s periphery, using reflective and absorber materials on opposite sides to finely regulate neutron flow and reactor power. This innovation is critical for MARVEL’s compact design—standing just 15 feet tall and 4 feet wide—enabling portability and rapid deployment while maintaining precise control of the reactor’s output. The transition from concept to hardware presented mechanical challenges, including higher-than-expected friction and backlash, which required redesigns such as larger gearheads and improved dampers to ensure rapid and reliable drum rotation, especially during emergency shutdowns (“scrams”). The RCS is built to rigorous NQA-1 nuclear quality standards and features tunability to