[en] In February 2008, a primary-to-secondary leak occurred at Fessenheim Unit No.2 on a steam generator. A circumferential fatigue crack was observed at the upper tube support plate level of the R12C62 tube although the stability ratio evaluation performed to take into account some prior international events, concluded that this tube had no risk of fluid-elastic instability. A new tube pull process was developed and performed by AREVA in 2011 just before the SG replacement. The extraction at the uppermost TSP elevation was a first occurrence in the French EDF PWR. Destructive examinations were carried out in the EDF hot laboratory of CEIDRE/Chinon in order to characterize damage mechanisms at the initiation and propagation stage. The document relates the major results of laboratory examinations leading us to exclude the fluid-elastic instability scenario as previously reported in North-Anna (1987) and Mihama (1991) tube rupture incidents. Results analysis with particular focus on the fracture surface description using Scanning Electron microscopy observations and metallurgical investigations provide new elements concerning the aggravating factors of fatigue damage. Fracture surface investigations reveal that the circumferential crack was due to high cycle fatigue with a very low stress intensity factor. Some aggravating factors like intergranular corrosion appeared to be critical for the fatigue cracking initiation stage. The deterioration was also largely promoted by the lack of tube support at the Anti-Vibration Bars