Requirements related to in-service inspection of reactor vessels

Abstract The in-service inspection of nuclear facilities should make it possible to detect all flaws capable of deterioration. The size of a flaw is not normally characteristic of its seriousness: a large, stable defect which is not developing is of no importance for the safety of the facility whereas a small but developing defect may be dangerous and hence of importance for safety. It is essential to detect all defects, so that any development they may be undergoing can be assessed, and to use, for that purpose, a technique with a maximum detection probability; but the main thing is to characterize all developing defects. For the in-service inspection of pressurized-water reactor vessels the “Commissariat a l'Energie Atomique” has conducted studies on inspection methods with a view to ensuring first the best possible detection and secondly the best possible characterization of flaws. Since 1973 many publications have appeared on the subject and this paper will only recall the essentials giving particular attention however to the characterization of defects, which is the principal purpose of the studies currently being conducted.