The U.S. Nuclear Regulatory Commission (NRC) is amending its spent fuel storage regulations by revising the Holtec International (Holtec) HI-STORM 100 dry cask storage system listing within the "List of Approved Spent Fuel Storage Casks" to include Amendment No. 7 to Certificate of Compliance (CoC) Number 1014. Amendment No. 7 will modify the CoC to add the HI-STORM 100U system to the HI-STORM 100 cask systems. The HI-STORM 100U system allows for the underground storage of dry spent nuclear fuel (SNF) by utilizing an underground vertical ventilated module (VVM) that can accept certain Holtec multipurpose canisters (MPCs) previously certified for storage of SNF in the aboveground HI-STORM system. The amendment also incorporates a mandatory radiation protection perimeter around the loaded VVMs. In addition, the amendment will reinstate the decay heat limits for damaged fuel and fuel debris in Appendix B, Technical Specification (TS) 2.4, for the aboveground system that had been inadvertently deleted from Amendment Nos. 5 and 6; incorporate separate TS Appendices A and B for the aboveground system (Apps. A and B) and for the HI-STORM 100U system (Apps. A-100U and B-100U); revise Appendix B, TS 3.4.5, to be consistent with the required system thermal boundary conditions, as submitted in the applicant's safety analysis report for a fire accident condition, and with Holtec's original (i.e., initial certificate application or Amendment 0) submittal and the NRC's original safety evaluation report; and revise and add certain definitions in Appendix A, TS 1.1, to include the VVM. The amendment will also incorporate minor editorial corrections in the TS for the aboveground system.