EFFECTS OF IRRADIATION ON INTERGRANULAR STRESS-CORROSION CRACKING

Intergranular stress corrosion cracking (IASCC) is a pervasive and gen eric problem in current light water reactor and advanced reactor desig ns that can lead to widespread component failure. IASCC is believed to be due to either to changes in the grain boundary composition, the mi crostructure or the water chemistry and corrosion potential. Of greate st interest are the changes in composition and microstructure since IA SCC exhibits a well-defined, although not invariant, dose threshold. C hanges in grain boundary composition are a result of radiation-induced segregation (RIS) and result in enrichment of nickel, depletion of ch romium as well as changes in the impurity element compositions at the grain boundary. Although the basic theory of RIS is believed to be und erstood, quantitative descriptions of observed changes are not yet pos sible 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 irradi ated yield strength have been found. However, a fundamental understand ing of the deformation mechanisms and the way in which deformation is coupled to IG cracking in alloys irradiated under LWR conditions (250- 360-degrees-C, 1-5 dpa) is lacking. Finally, although radiation is kno wn to affect IGSCC through changes in water chemistry and corrosion po tential, it is not a necessary condition. Overshadowing and slowing pr ogress on this important problem is a lack of well-defined-data from p roperly irradiated and properly characterized materials, due principal ly to inherent experimental and financial difficulties. As such, the s pecific mechanism(s) of IASCC remain unknown.