Duke Power Company has experienced high levels of steam generator tube degradation at its McGuire Nuclear Station, Units 1 and 2, and at Catawba Nuclear Station, Unit 1. Repair of the degraded tubes by sleeving and plugging has resulted in exceeding the tube plugging levels assumed in the licensing basis analyses. Consequently, the licensing basis was reanalyzed with the U.S. Nuclear Regulatory Commission-approved RETRAN-02 and VIPRE-01 methodology to justify continued operation with tube plugging levels up to 20%. A decision was also made to replace the steam generators with a design significantly different from the current steam generators. This necessitated additional analytical efforts to determine the thermal-hydraulic transients to be used in the design of the replacement steam generators, to reanalyze the licensing basis, and to re-certify the control room simulator. The RETRAN-02, RETRAN-03, VIPRE-01, GOTHIC 4.0, and RELAP5/MOD3 codes were used for these analyses. The adverse impact of increased steam generator tube plugging levels and the design of the replacement steam generators were accommodated without significantly impacting plant operation or requiring more restrictive technical specification limits.