Root Cause Analysis of In-Situ AP1000 Reactor Coolant Pump Lock Cup Failure

The failure of the large-scale canned motor reactor coolant pump (RCP) of Sanmen Unit 2 caused the unit to shut down in the first cycle of operation. In order to analyze the causes of the RCP fault, based on the fault characteristics and cause analysis methodology, this paper develops the RCP fault root cause analysis method. Through the RCP manufacturing record investigation, on-site operation data evaluation, disassembly and inspection forensics analysis, design analysis and test verification, root cause analysis and evaluation, the root cause of the RCP failure is confirmed that the lower thrust runner lock cup is affected by the resonance flow induced vibration. The initial flaw continues to expand under the action of the resonance and eventually separates. The lock cup fragment makes two holes on the stator can and eventually leads to the RCP failure. The root cause analysis method established in this study can be used for the analysis and treatment of similar complex problems.