Review of Responses to NRC Bulletin 2003-02-Leakage from Reactor Pressure Vessel Lower Head Penetrations and Reactor Coolant Pressure Boundary Integrity

Cracking in pressurized water reactor (PWR) bottom mounted instrumentation (BMI) fabricated from Alloy 600 base material was first identified at the South Texas Project, (STP) Unit 1 plant in the United States (US). Based on the failure analysis of the BMI, the licensee concluded that the cracking was due to primary water stress corrosion cracking (PWSCC). PWSCC has been identified as the primary degradation mechanism affecting PWR high nickel alloy nozzles and welds (e.g., Alloy 600 tubing, piping, or forging material, and Alloy 82/182 weld material) in the reactor coolant system. To address these concerns, the Nuclear Regulatory Commission (NRC) issued NRC Bulletin 2003-02, "Leakage from Reactor Pressure Vessel Lower Head Penetrations and Reactor Coolant Pressure Boundary Integrity,” on August 21, 2003, to all holders of operating licenses for PWRs. The purpose of the bulletin was to request information from the industry related to the structural integrity of the reactor pressure vessel BMI nozzles at PWR facilities. This report summarizes the NRC staff’s review of licensee responses to the Bulletin, licensee’s BMI inspection results, industry activities related to BMI inspections, and the staff’s conclusions regarding the need for additional regulatory action in this area. A brief summary regarding the inspection results of the BMI penetrations and the associated aging monitoring programs for the foreign reactors is included in this report. Read more