Dry cask storage is the passive, long-term storage method for spent nuclear fuel that has cooled sufficiently in a spent fuel pool (typically after 5-10 years) to be transferred to sealed steel canisters housed within concrete or steel overpacks. The canisters provide radiation shielding and structural protection, while natural air convection through vents in the outer overpack removes residual decay heat without any active cooling systems, electrical power, or water supply. Each cask typically holds between 24 and 37 spent fuel assemblies, weighing 100-180 tons when loaded. Dry cask storage has been deployed since the 1980s and is now used at every U.S. nuclear power plant site, with an excellent safety record spanning decades of operation through earthquakes, hurricanes, floods, and other external events.
Holtec International, one of the leading SMR developers, is also the world's dominant manufacturer of dry cask storage systems. Holtec's HI-STORM and HI-STAR storage and transport cask systems are deployed at the majority of U.S. nuclear plant sites. This dual role in both reactor development and spent fuel management gives Holtec a unique perspective on the complete nuclear fuel cycle. The company's Palisades site in Michigan, where it plans to deploy twin SMR-300 units, already contains an existing Independent Spent Fuel Storage Installation (ISFSI) with dry casks from the original reactor's operations. The Palisades restart (the first-ever U.S. commercial reactor restart, targeted for mid-2026) and the SMR-300 program will add to this spent fuel inventory over time.
For SMR deployments, dry cask storage requirements are a site planning consideration that affects facility footprint, decommissioning costs, and long-term financial obligations. Smaller reactor cores and higher fuel burnup in some advanced designs may reduce the total number of spent fuel assemblies generated per unit of energy, potentially reducing long-term dry cask storage needs. However, HALEU-based spent fuel may have different regulatory requirements for storage and transportation due to higher fissile content and different isotopic profiles. The industry continues to pursue consolidated interim storage facilities (such as those proposed by Holtec in New Mexico and Interim Storage Partners in Texas) that could centralize spent fuel management away from reactor sites, but these projects face ongoing regulatory and political challenges. Until a permanent geological repository or advanced reprocessing capability becomes available, dry cask storage remains the de facto long-term management solution for the U.S. nuclear fleet and future SMR deployments.