A reactor vessel upper head contains numerous penetrations to allow the insertion of the control rod drive mechanism to regulate the nuclear reaction. Some plants have alloy 600 material used to penetrations and alloy 182 employed to the J-groove partial penetration welds. The head base material is a low-alloy steel with stainless steel clad. Cracks were detected in the penetrations base metal and welds, including throughwall cracks, from stress corrosion cracking (SCC). Therefore, an inspection and analysis program were adopted to manage SCC. This program relies on ultrasonic methods to characterize cracks, numerical analysis to estimate the residual stresses from welding, and fracture mechanics to calculate the crack growth over operating time. The analysis for this situation was consolidated in the ASME Code Section XI Appendix O. A numerical application is examined, with total stresses obtained in the weld region. The crack propagation is stablished to determine if the penetration can remain in service or if it must be repaired.