A refueling outage is the planned shutdown of a nuclear reactor for the purpose of removing irradiated (spent) fuel assemblies from the core and loading fresh fuel to sustain operation for the next fuel cycle. In conventional light-water reactors, refueling outages occur every 18-24 months and typically last 20-35 days, during which approximately one-third of the core's fuel assemblies are replaced while the remaining assemblies are shuffled to optimize fuel utilization. The outage duration directly impacts the plant's capacity factor and annual revenue: each day of outage beyond the minimum required represents lost electricity production valued at hundreds of thousands to millions of dollars depending on market prices and plant output.
SMR designers have pursued multiple strategies to minimize or eliminate refueling outage impacts. NuScale's VOYGR multi-module architecture allows individual 77 MWe modules to undergo refueling while other modules continue operating, maintaining high plant-level output throughout the maintenance campaign. A 12-module VOYGR plant could stagger module refueling to maintain near-continuous output at a reduced level rather than experiencing complete plant shutdowns. The BWRX-300 at Darlington targets streamlined outage procedures leveraging GE-Hitachi's extensive BWR refueling experience. Some advanced designs pursue extended fuel cycles: TerraPower's Natrium is designed for longer core residence times enabled by HALEU metallic fuel, and Kairos Power's KP-FHR uses a pebble bed design that could potentially enable online refueling, where fresh pebbles are added and spent pebbles removed continuously without shutting down the reactor.
At the extreme end of the spectrum, microreactor designs aim to eliminate conventional refueling entirely. Westinghouse's eVinci heat pipe reactor is designed for a multi-year core life with factory refueling, meaning the entire reactor module would be returned to the factory for core replacement rather than performing on-site fuel handling. Radiant's Kaleidos microreactor similarly targets an extended core life before factory replacement. Oklo's Aurora envisions refueling intervals measured in decades. These approaches trade fuel cycle efficiency for operational simplicity, eliminating the need for on-site spent fuel handling equipment, refueling cranes, and the specialized workforce required for conventional outage execution. For behind-the-meter applications at data centers and remote sites, the elimination of refueling outages represents a significant operational advantage and cost reduction.