[en] Serious leaks were detected in the inlet and outlet pipes of the heat exchangers in the primary cooling loop of the nuclear reactor in 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 was concluded that stress-corrosion cracking was the main mode of failure, while minor evidence of fatigue was encountered as well. Measures for the prevention of similar failure in the future are suggested. (Author)