Materials Options for the Steam Generator of Sodium Cooled Fast Reactors

Ferritic steels are the most preferred materials for steam generator (SG) applications in sodium cooled fast reactors (SFRs) due to their high resistance to aqueous stress corrosion cracking and enough high strength properties. Among the ferritic steels, 2.25Cr-1Mo (T22), 2.25Cr-1.6W (T23) and Modified 9Cr-1Mo (T91) were considered as the structural materials for the SG. A series of tests (including corrosion tests in sodium, high temperature high pressure water and high temperature water vapour) on these materials was performed by the China Institute of Atomic Energy. The final option for structural material for SG must consider service life in the SFR. A method to evaluate the performance of the SG was developed by calculating the lifetime arrangement of heat transfer tubes in the superheater, while the other issues such as sodium corrosion, decarburization, steam corrosion and creep damage at service temperature had to be taken into account. The analysis result shows that T22 steel is suitable as an SG structural material when the design lifetime of the reactor is 20–30 years, while T23 steel is suitable for 40–50 years and T91 has most advantages when the lifetime is extended to 50–60 years. (author)