email questions or comments to the author(s) at Keith Moser: keithm3510@aol.com

Abstract
During routine maintenance, cracks were observed in the 1C Residual Heat Removal pump impeller at the South Texas Nuclear Project. This impeller was immediately replaced and other pump impellers were inspected; however, due to the number of Emergency Core Cooling impeller manufactured from the same material, a detailed metallurgical evaluation was conducted. This evaluation was followed by fracture mechanics analysis to determine the suitability of case martensitic stainless steel impellers containing numerous stress corrosion cracks (SCC). Difficulties in evaluating the values and the common belief that weld repairs or flame hardened surfaces above 30 HRC will crack due to SCC irrespective of the surrounding base metal properties. This report details the metallurgical evaluation, hardness testing and residual stress measurements used to predict the likelihood of SCC. This report also contains additional fracture toughness testing and corresponding fracture mechanics analysis used in determining the suitability of Martensitic Stainless Steel Impellers.