Failure of welded pipe in the cooling system of a nuclear reactor

Routine inspection of the cooling system of a nuclear reactor at the Nuclear Research Centre-Negev in Israel detected serious leaks of heavy water in both the inlet and outlet pipes of the primary coolant heat exchangers. After disassembly, the heat exchanger was submitted to a series of nondestructive tests, which included ultrasonic, dye penetrant, and radiographic inspections. A flawed part was found, removed, mechanically tested, and examined. The cracked areas of the Inconel 600/sup 2/ tube were studied using optical and scanning electron microscopy. Chemical analyses of both cracked and intact tubes were carried out. Stress-corrosion cracking was determined to be the main mode of failure; minor evidence of fatigue was also encountered. This paper describes the investigation that determined the cause and location of the cracks and suggest measures to prevent their reoccurrence