Human error probabilities from operational experience of German nuclear power plants

We report about a project aimed to collect human reliability data from the operational experience of German nuclear power plants. Its objective is the validation and extension of existing human reliability databases (in particular, the THERP database). A method utilizing the German licensee event report system to gather the data is described. For certain tasks with specific attributes this method allows to determine the number of times the task was performed in the past, as well as the number of errors that occurred. A statistical method to estimate the corresponding human error probability (HEP) based on these numbers is provided. We have applied this method to the reportable events stored in the database collecting the reportable events in German nuclear installations. In this way up to now 37 HEPs for a wide variety of tasks were obtained, together with information about relevant performance shaping factors. We discuss these HEP estimates and compare them to the THERP database if it provides a HEP for the task in question. In all except three cases we find an agreement within the uncertainty bounds. Moreover, we contribute 21 HEP estimates for which the THERP handbook provides no data, so they serve to extend the THERP database, among them a number of memory related errors. Therefore, this data may serve as an input for the discussion of second generation HRA methods.