Kinetics of Corrosion Product Release from Carbon Steel Corroding in High-Temperature, Lithiated Water

An experiment to measure the release of Fe-59 radiotracer from an irradiated carbon steel tube in a loop containing flowing lithiated water at 270°C to 280°C was conducted. Measurements were made on-line by monitoring with a gamma spectrometer the radioactivity collected downstream of the tube on a bed of granular magnetite. When logarithmic corrosion kinetics were assumed, the release was described very well by a mathematical model that assumes competition for the radiotracer between incorporation in the oxide precipitating on the tube surface and mass transport to the bulk fluid. The logarithmic expression also fit data obtained gravimetrically from carbon steel tubes exposed in a separate experiment reasonably well. The distinction between apparent release, as measured with a radiotracer, and actual net release, which should not occur in a system saturated with dissolved corrosion products, was emphasized.