Defining accident sequences for conducting probabilistic risk assessments

A major portion of any PRA activity is devoted to the identification of potential accident sequences which could lead to radiological releases. A systematic application of acceptable methods and techniques is desirable. Event tree and fault tree analysis form the basis for plant/system modeling. Consensus approaches for acquisition of information, model development, assumptions, constraints, inclusion of common cause events, interrelationships of event trees and fault trees, accuracy, completeness and manner of documentation are presented. Alternative methods which may be used or directed toward a specialized purpose are also of interest. Particular emphasis is placed on defining in practical terms the specific tasks of accident sequence definition and what is required, why it is necessary and how each task relates to the overall risk assessment process