Effects of irradiation on intergranular stress corrosion cracking

Intergranular stress corrosion cracking &YSCC) is a pervasive and generic problem in current light water reactor and advanced reactor designs that can lead to widespread component failure. IASCC is believed to be due to either to changes in the grain boundary composition, the microstructure or the water chemistry and corrosion potential. Of greatest interest are the changes in composition and microstructure since IASCC exhibits a well-defined, although not invariant, dose threshold. Changes in grain boundary composition are a result of radiation-induced segregation (RIS) and result in enrichment of nickel, depletion of chromium as well as changes in the impurity element compositions at the grain boundary. Although the basic theory of RIS is believed to be understood, quantitative descriptions of observed changes are not yet possible and hinder the correlation between RIS and IASCC. Changes in the microstructure are intimately linked to the strength and ductility of the irradiated alloy and strong correlations between IASCC and irradiated yield strength have been found. However, a fundamental understanding of the deformation mechanisms and the way in which deformation is coupled to IG cracking in alloys irradiated under LWR conditions (25636O’C, 1-5 dpa) is lacking. Finally, although radiation is known to affect IGSCC through changes in water chemistry and corrosion potential, it is not a necessary condition. Overshadowing and slowing progress on this important problem is a lack of well-defined-data from properly irradiated and properly characterized materials, due principally to inherent experimental and financial difficulties. As such, the specific mechanism(s) of IASCC remain unknown.