- Serious leaks were detected in the inlet and outlet pipes of the heat exchanger in the primary cooling loop of the nuclear reactor at the NRCN. Non-destructive tests were conducted which included: ultrasonic testing, tests with dye penetrants and radiography. The flawed part was replaced and mechanical tests were performed on it. The crack areas of the Inconel 600 tube were examined using optical and scanning electron microscopy. Chemical analysis of both cracked and intact tubes were carried out. It is concluded that stress- corrosion cracking was the main cause of failure, while minor evidence of fatigue was encountered as well. Measures for the pre\'ention of similar failure in the future are suggested.