Defect flow analysis of control-rod-drive operational events

A defect flow analysis of License Event Report data involving control-rod (CR) and control-rod-drive mechanism (CRDM) operational events was conducted to extract the lessons to be learned from the past experience of light water nuclear reactors operating in the United States. The results of the analysis are used to formulate characteristics of CR/CRDM defects. Among those formulated are (1) the leading direct causes of defects are inadequate design and inadequate operator training, (2) a relatively large number of defects are systematic, and (3) defects that result in system failure are rare. The analysis results indicate that most defects could easily have been prevented