Trending of Low Level Events and Near Misses to Enhance Safety Performance in Nuclear Power Plants

The number of important and significant events in nuclear power plants (NPPs) is decreasing, and current world industry indicators demonstrate that this has become true throughout the nuclear industry. This is important for the survival and acceptance of the nuclear industry; however, these indicators could hide the existence of a multitude of events which are of lower significance and even near misses (a term from the aviation industry to denote ‘almost accidents’) that have not been captured by the existing detection methods and thresholds. The main objective of this publication is to provide examples, methodologies and suggestions to NPP operators on how to implement a procedure to detect, select and process such events. International experience shows that the number of such events ranges from 2000 to 5000 per operating reactor year. Too many plants do not detect or report these low level events. However, these events are the submerged part of the iceberg and must be considered by the operating unit.