Abstract
Our previously described coupled environment fracture model (CEFM) for intergranular stress corrosion cracking (IGSCC) and irradiation-assisted stress corrosion cracking (IASCC) in light water reactor heat transport circuit components has been extended to consider steel corrosion, the oxidation of hydrogen, and the reduction of hydrogen peroxide, in addition to the reduction of oxygen (as in the original CEFM), as charge transfer reactions occurring on the external surfaces. Additionally, we have incorporated several theoretical approaches to estimate the crack tip strain rate. The key concept of the model is the coupling between the internal and external environment involving all those variables that are observed to have a significant role in crack growth (e.g. flow velocity in the pipe, conductivity, crack length, stress intensity, corrosion potential, temperature, etc.). We have also explored the use of Poisson's equation coupled to Fick's second law of diffusion for calculating the concentrations and fluxes of all seven species considered in the model, instead of using Laplace's equation coupled to Fick's first law, as was previously done. The overall results are little different. The model provides rational explanations for the effects of oxygen, conductivity, stress, and hydrogen (as used in hydrogen water chemistry in BWRs) on the rate of crack growth in sensitized Type 304 in simulated LWR invessel environments, and we propose that the CEFM can serve as the basis of a deterministic method for estimating component life times.
