LMFBR Steam Generators: Behavior of Heat Exchange Tubes Faced with a Through Crack Resulting in Contact Between Sodium and Water

An Electricité de France survey on the behavior of cracked tubes under operating conditions of an industrial steam generator was conducted. A comparison was first made of the development kinetics of the cracks according to the type of material: Incoloy 800, Cr—1 Mo, 9 Cr—2 Mo, and to the initial leak. Then, two successive stages are evidenced in the self-development process of a water leak into sodium:

1. an incubation stage, during which the material is subject to intense corrosion in the crack area
2. a self-erosion stage, marked by the appearance of a leak rate that grows slowly at first, then suddenly, when the tube wall near the crack gives way under pressure.