The Nuclear Regulatory Commission (NRC) is amending its regulations revising the NAC International, Inc., NAC-UMS Universal Storage System listing within the "List of approved spent fuel storage casks" to include Amendment No. 4 to Certificate of Compliance (CoC) Number 1015. Amendment No. 4 to the NAC-UMS CoC will modify the cask design by replacing the specific term "zircaloy" with the more generic term "zirconium alloy"; revising the definitions of "operable" and "site specific fuel"; revising vacuum drying pressure and time limits; revising short-term temperature limits and completion times for the heat removal system; clarifying the surface dose rate surveillance; adding a dissolved boron concentration option; deleting a redundant boron concentration administrative control; adding an alternate site-specific design basis earthquake analysis; and incorporating editorial and administrative changes.