Modeling of the Electrochemistry of Stress Corrosion Cracks in Sensitized Type 304 Ss in Boiling Water Reactors

Abstract A physico-electrochemical model has been developed to describe intergranular stress corrosion cracking (IGSCC) in sensitized Type 304 stainless steel (SS) in simulated BWR recirculation environments. This model differs from previously reported models in that the internal and external environments are coupled by the need to conserve charge in the system. Thus, solution of Laplace's equation for the external environment, assuming that oxygen reduction on the external surfaces consumes the positive current emanating from the crack mouth, yields a boundary condition for solving Laplace's equation for the internal crack environment. Metal dissolution at the crack tip is described by the slip dissolution model, with the frequency of rupture of the passive film being a strong function of the stress intensity factor. The reduction of oxygen on the external surfaces is described in terms of a general Butler-Volmer equation that incorporates mass transport and charge transport phenomena. In this way, the model incorporates the effects of oxygen concentration, flow rate, and the conductivity of the external environment as well as accounting for the effect of stress on crack growth.