Contribution of Human Reliability in Power Probabilistic Safety Assessment Models Versus Shutdown Models

Human reliability analysis is a method, which evaluates the human error probabilities of human failure events, which may arise when human actions are required in operation of the considered facility or system. The objective of the work is to show the contribution of human failure events in probabilistic safety assessment with focus on comparison of this contribution over the different plant operating states. The method integrates the diagnosis and action part, which are evaluated for all steps, which are needed for modeling of the human action under investigation considering the parameters, which impact the human failure probability and which are obtained from database. The results show that the risk contribution of human failure events is notably higher in low power and shutdown states than in full power operation. The results show that the human factor in shutdown plant states is the most important risk contributor regarding the contribution to the core damage frequency and regarding the risk reduction worth and risk achievement worth. Only at some plant operating states, some other groups of equipment show larger risk achievement worth than group of human failure events.