sentences:  Some hope that the casks can be used for 100 years but cracking related to corrosion could occur in 30 years or less.Robert Alvarez, a former Department of Energy official who oversaw nuclear issues, said Dry cask storage would provide safer storage until a permanent nuclear repository was built and loaded, a process that would take decades.At places like Maine Yankee, Connecticut Yankee and Rancho Seco, reactors no longer operate, but the spent fuel remains in small concrete-and-steel silos that require maintenance and monitoring by a guard force.