Failure analysis on speed reducer shaft of sluice gate in nuclear power plant

Irradiated fuels of nuclear power plants are usually preserved and cooled in specific water pools containing boric acid solution in nuclear power plants because of residual radioactivity and radiated heat. A sluice gate between two storage pools is used for isolation and connection of irradiated fuels. However, suddenly happened an abnormal fracture of a speed reducer shaft for driving sluice gate in a nuclear power plant with 650 MW capacity in the southern part of China, which could cause potential risk for storage safety of the fuel assemblies. Therefore, comprehensive analysis and investigation on the fractured shaft were carefully carried out in this study. The analysis results revealed that hydrogen embrittlement and temper brittleness induced during carburization and heat treatment were the root causes for the unexpected fracture of the shaft. Countermeasures and recommendations were then proposed and proved effective after implementation.