Operator-action trees, a method for modeling cognitive errors in risk analysis

A method has been developed for modeling cognitive errors by nuclear-power-plant operators during accident conditions. It has been developed for application in probabilistic risk assessments. It is contrasted with previously used methods of humanreliability analysis in that it takes a holistic approach, since analyses of real-world accidents reveal that the mechanistic kinds of human error are a minor feature of catastrophes. The method itself is at an interim stage of development; it is being applied in two ongoing probabilistic risk assessments, where it has been found simple to apply and yields results which seem realistic. This method forms the basis for much of the contents of the recently published NUREG/CR-3010