Review of recent events involving setpoint drift in safety and safety/relief valves at U.S. nuclear power plants

Watanabe, Norio

Since the beginning of 1980's, in the United States, there have been many reports involving setpoint drift of the safety or safety/relief valves. The United States Nuclear Regulatory Commission (NRC) has issued the generic communications on this issue and the industry has made their efforts to identify the causes and to take corrective actions. However, the NRC staff found that from 2001 through August 2006, over 70 licensee event reports (LERs) involved instances where safety or safety/relief valves failed to meet the allowed lift setpoint tolerance and issued the Information Notice 2006-24 in 2006 to alert licensees of operating experience insights associated with the safety and safety/relief valves exceeding the lift setpoint tolerance. This report provides the description on the historical NRC's responses to safety and safety/relief valve issues including setpoint drift and analyzes the trends of the ninety-four events, reported as LERs, involving setpoint drift at U. S. nuclear power plants during the years from 2000 to 2006.