Technical Basis Part 1 for Code Case N-889: Data Selection and Modeling of Stress Corrosion Crack Growth Rates for Irradiated Austenitic Stainless Steels in Light Water Reactor Environments

Abstract

Abstract A multiyear international data collection, data review, modeling, and implementation project was recently completed, producing stress corrosion crack growth rate (CGR) models and reference curves for irradiated austenitic stainless steels in light water reactor (LWR) environments. The curves have been approved as ASME B&PV Section XI Code Case N-889, and this paper is the technical basis Part 1 for Case N-889, summarizing collection, review, and selection of calibration data, modeling, and analysis of fit. Over 800 CGR data points were collected from six laboratories worldwide, an international expert panel reviewed and ranked the data, and the better-ranked data were used to calibrate empirical models for irradiation-assisted stress corrosion cracking (IASCC) CGR in boiling water reactor (BWR) normal water chemistry (NWC), BWR hydrogen water chemistry (HWC), and pressurized water reactor (PWR) primary water environments. This Part 1 paper also discusses related literature and compares with other data not used for mean model calibration. A technical basis Part 2 paper describes shifting the mean models to the 75th percentile, simplifying to produce Case N-889 reference curves, and comparing with previous reference curves and over 500 data points not used for reference curve development, including weld, cast, and heat affected zone (HAZ) materials, additional wrought laboratory data, and field data from repeated inspection of BWR core shrouds. Part 2 also describes the irradiated yield stress model in Case N-889, compares that model with its calibration data and other data not used for calibration, and presents example calculations.