Steam generator tube cracks at Dampierre 1 EDF PWR plant - impact on plant safety

During later shutdowns, in 1985 and 1986, a further 27 tubes were removed from Dampierre 1 to monitor the trends of these small cracks and to make sure that the numerical forecasting model used for the mechanical behaviour remained conservative for actual tubes. A total of 31 tubes were removed from the three Dampierre 1 steam generators on both hot and cold sides (4 on the cold side). These were alloy 600 tubes which had not undergone heat treatment at 7000C. They had undergone full-depth rolling as well as kiss rolling. Table 1 shows the leading data concerning the tubes removed due to stress corrosion cracking at roll transition: Steam generator, tube manufacturer, date of removal, period of service on the nuclear unit and the reason for removal. The tubes were selected on the basis of eddy current testing results using an axial probe and a long rotating probe. (orig./GL)