[en] This report reviews the significant variables of flaw depth, length, location and orientation required for fracture mechanics evaluations of pressure vessel integrity. Results of calculations are presented which emphasize pressurized thermal shock (PTS) and the significance of flaws located at or near the inside surface of the vessel. For PTS conditions, previous studies have shown that vessel failure probability is relatively insensitive to flaw depth. In this study the impact of flaw length is also evaluated, indicating the importance of fully characterizing all flaw dimensions by NDE. Results of other evaluations are presented, showing the importance of accurately locating flaws by NDE. The influence of vessel cladding is emphasized, with the relative significance of flaws through the clad and at various depths below the clad being addressed