Theoretical Estimation of Crack Growth Rates in Type 304 Stainless Steel in Boiling-Water Reactor Coolant Environments

The coupled-environment fracture model (CEFM) for inter-granular stress corrosion cracking (IGSCC) of sensitized type 304 (UNS S30400) stainless steel (SS) in light-water reactor (LWR) heat-transport circuits was extended by incorporating steel corrosion, hydrogen (H2) oxidation, and hydrogen peroxide (H2O2) reduction in addition to oxygen (O2) reduction as charge-transfer reactions occurring on the external surfaces. A theoretical fracture mechanics approach was incorporated to estimate the crack-tip strain rate, and a void nucleation model was included to account for ductile failure at very negative potentials. In the CEFM, coupling between the internal and external environments and the need to conserve charge are the key physical and mathematical constraints that determine the rate of crack advance. The model provides rational explanations for the effects of O2, H2O2, H2, conductivity, stress intensity, and flow velocity on the crack growth rate (CGR) in sensitized type 304 SS in simulated LWR in-vessel environments. The CEFM was proposed as the basis of a deterministic method for estimating component lifetimes in LWR heat-transport circuits.