This report addresses Generic Safety Issue (GSI) 188, "Steam Generator Tube Leaks or Ruptures Concurrent with Containment Bypass from Main Steam Line or Feedwater Line Breaches," which concerns the potential for additional tube leakage or ruptures from the growth of existing cracks in steam generator tubes resulting from the dynamic loads following a main steam line break (MSLB) or feedwater line break (FWLB). To address the issue, this report provides the technical findings from thermal-hydraulic transient analyses and sensitivity studies, a simplified finite-element model of steam generator support structures and tubes, and structural analyses and sensitivity studies of the potential for crack growth. The results show that the additional dynamic loads from an MSLB are greater than those from an FWLB. The report concludes that dynamic loads from an MSLB are low and do not affect the structural integrity of tubes and do not lead to additional leakage or ruptures beyond what would be determined using differential pressure loads alone. Therefore, GSI-188 is closed, and the staff recommends no changes to existing regulations or guidance with respect to the dynamic loads induced by a breach of the main steam or feedwater line.