Evaluation of Stress Corrosion Crack Growth in Low Alloy Steel Vessel Materials in the BWR Environment

Abstract

Low alloy steels (LAS) used in the fabrication of reactor pressure vessel (RPV) and nozzles have been resistant to stress corrosion cracking (SCC) in the Boiling Water Reactor (BWR) environment. The plate material is SA533 Grade B and the nozzle material is SA508 Class 2 for most operating BWRs. While BWR service field experience with the LAS materials has been very good for there have been a limited number of SCC incidents where cracking has been reported especially in Alloy 182 RPV attachment (dissimilar metal) welds. This paper describes the methodology for the assessment of SCC crack growth rate (CGR) of LAS RPV components in the BWR environment. Specifically, it describes the development of CGR disposition lines (also called reference crack growth rate curves) for normal water chemistry (NWC) and hydrogen water chemistry (HWC) in BWR environments. In addition, based on more recent data from tests on the effect of chloride transients in NWC environments are also proposed.