A study on human errors related to NPP maintenance activities

This experience-based study on human errors in nuclear power plant (NPP) maintenance used about 4400 maintenance history records and licensee event reports of an NPP from the years 1992-94 as its material. The aims of the study were to identify common cause failure mechanisms, allow statistical treatment and generate numerical safety indicators. About 30 dependent failures were identified for in-depth root cause analyses. The instrumentation is very prone to human errors. Most errors stem from the refueling outage period, and about half of them were identified during the same outage. Plant modifications are an important source class. Enhanced coordination and review, post-installation checking and start-up testing programs of these projects might decrease the amount of dependent errors