Gen Nakayama

Monte Carlo Simulation Based on SCC Test Results in Hydrogenated Steam Environment for Alloy 600

We investigated the applicability of a stress corrosion cracking (SCC) engineering model and simulation method developed on the basis of the SCC of sensitized 304 stainless steel in a simulated BWR environment to the primary water stress corrosion cracking (PWSCC). We conducted a uniaxial constant loading test on Alloy 600 in a 400 °C hydrogenated steam environment and found that the number of cracks observed on a specimen surface after every passage of 450 h could be approximated to Poisson distribution, indicating that a Poisson random process model is applicable to the SCC in this system. By applying the engineering model, we statistically processed experimental data by assuming that the time distribution of occurrence of microcracks follows exponential distribution, and then obtained input data for the SCC simulation. Using coalescence coefficient, k, as a fitting parameter to obtain a reasonable k-value, it was found that the best agreement between the experimental and simulation results for the number of microcracks and the maximum crack length at k = 0.15. This is about one third the k-value of 0.5 found in sensitized 304 stainless steel in the BWR environment, indicating that coalescence is more subdued in PWSCC than in SCC in the BWR environment.