Pulsed E-beam modified FeCrAlY corrosion barriers for future fast reactor systems

Compatibility problems of structural materials (steels) with the coolant are one of the key issues for the development of lead alloy fast reactors. For future sodium cooled fast reactors lead alloy cooled intermediate heat exchangers are investigated to minimize the risk of sodium water interaction. Dissolution of metallic components into the lead alloy and extensive oxide scale growth are challenges that have to be met for both systems. Oxide scales formed on steels act as diffusion barriers for cations and anions and provide the best protection against dissolution attack. At temperatures above 500oC austenitic steels suffer from severe dissolution attack, while martensitic steels form thick oxide scales, which hinder heat transfer from the fuel pins and which may break off and eventually lead to a blocking of the coolant channel. Above 500oC steels have to be protected by stable, thin oxide scales. A well understood measure is the alloying of strong oxide formers like aluminium (Al) into the surface that combine protection against dissolution with slow growing oxide scales. An Al-content between 4 and 10 wt% is known to be sufficient for selective formation of alumina scales that grow only very slowly due to low diffusion coefficients for cations and anions. Coating the surface with an Al-alloy with subsequent GESA treatment is the method used for this process. A number of corrosion experiments showed the good protective behavior of Al-scales in LBE with 10-6 wt% oxygen up to 650oC and for exposure times up to 10000 h. Furthermore the influence of parameters like stresses in the cladding wall, creep behavior, different flow velocities of the LBE and changing temperatures and oxygen concentrations in LBE is discussed. (author)