Modeling of Human Error for a Seismic PSA

Abstract

This paper describes a model for human error probability (HEP) for seismic probabilistic safety assessments (PSAs) of nuclear power plants and its application. Considering the factors unique to seismic events such as level of seismic motion and stress to the operators, the authors adopted a model called a limited ramp model (LRM), where HEP is assumed to be the same as that for internal event PSAs for zero level of seismic motion, and then increases linearly with seismic level to a constant at a certain seismic level. This model was applied to estimate the effect of human error on core damage frequency (CDF). Here, operator actions in the accident sequences initiated by loss of offsite power were categorized into two groups, short term actions and medium/long term actions, and parameters of the LRM for the HEP for each action were determined from available information on shaking table tests and an existing human reliability analysis method. The results showed that the effect of human error on the CDF was not significant for this case and indicated that, the modeling approach presented here is useful for examining the importance of various operator actions in seismic events.