Development of Structural and Steam Generator Materials for Sodium Cooled Fast Reactors

Nitrogen-alloyed low-carbon grade type 316L(N) SS is the principal material for high temperature structural components of the Prototype Fast Breeder Reactor (PFBR). Creep, and low cycle fatigue (LCF) properties of 316L(N) stainless steel base metal, weld metal and weld joints have been evaluated and found to fully meet the properties assumed in the design of PFBR components. In-sodium experiments have shown that flowing sodium has no detrimental effect on the creep and LCF properties of 316L(N) SS. Modified 9Cr-1Mo is the steam generator material of PFBR. Creep behaviour of indigenously produced modified 9Cr-1Mo steel and its weld joint have been characterized. The mechanism of degradation of creep rupture strength of modified 9Cr-1Mo steel weld joint due to type IV cracking has been established.