Model calculation of crack growth rate coupled to crevice chemistry for BWR plant life management

A calculation model for crack water chemistry-based crack growth rate (CBC) of intergranular stress corrosion cracking of structural materials in a boiling water reactor environment has been developed. This model was composed of three parts: (1) bulk water chemistry calculation, (2) crack water chemistry calculation, and (3) crack growth rate (CGR) calculation. Bulk water chemistry was calculated with a radiolysis model. In the CBC model, crack water chemistry calculation part can treat diffusion of chemical species, electrophoresis of ions, radiolysis, chemical reactions, and corrosions. Also, the CGR was calculated by metal dissolution rate at the crack tip which was driven by the cathodic reaction of oxidants. Crack tip dissolution rate was assumed to be governed by the square of the stress intensity factor. The CBC model could reproduce CGR dependence of sensitized type 304 stainless steel on electrochemical corrosion potentials and oxidant concentrations. When the CBC model was applied to evaluation of CGR on the core shroud, it was clarified that the crack water chemistry strongly affected the number of detected flaws. (author)