Case histories of failures in heat exchangers experience of Nuclear Power Corporation

Heat exchanger tubes are important components of nuclear power stations, whether they are part of the primary heavy water loop or of light water secondary loops. Exchanger tube failure can trigger plant outages and cause significant economic losses. In some of these exchangers, failure of tubes degrades one of the multiple protective layers guarding against accidental release of radioactivity to the environment and hence there are stringent requirements limiting leakage. Various tube degradation mechanisms have been identified during pre-service (PSI) and in-service (ISI) and during manufacturing stage inspections. Each case has been analysed in detail and corrective actions, appropriate to the occasion, have been implemented. Remedial actions have included design changes, material changes, changes to manufacturing and inspection methods, changes to operating parameters in addition to the obvious tube plugging recommendations. A few selected cases are detailed in this paper. 1 fig., 1 ill