Treatment of operator actions in the HTGR risk assessment study

Methods are presented for the treatment of operator actions, developed in the AIPA risk assessment study. Some examples are given of how these methods were applied to the analysis of potential HTGR accidents. Realistic predictions of accident risks required a balanced treatment of both beneficial and detrimental actions and responses of human operators and maintenance crews. Th essential elements of the human factors methodology used in the AIPA study include event tree and fault tree analysis, time-dependent operator response and repair models, a method for quantifying common cause failure probabilities, and synthesis of relevant experience data for use in these models.