Gareth W. Parry’s research while affiliated with Norrlands universitetssjukhus and other places

This paper discusses the issue of the characterization of uncertainty in a Probabilistic Risk Assessment (PRA) of a complex system, such as a nuclear power plant. The significance to the interpretation of the results of a PRA of maintaining the distinction between the aleatory and epistemic components of uncertainty is illustrated using a simple example. The point of view presented here is that the degree to which it is necessary to invoke both aspects of uncertainty to characterize an event in a PRA model is as much a function of the way the analyst chooses to model the event of interest as it is of the nature of the event itself.

This paper discusses why an improved Human Reliability Analysis (HRA) approach for use in Probabilistic Safety Assessments (PSAs) is needed, and proposes a set of requirements on the improved HRA method. The constraints imposed by the need to embed the approach into the PSA methodology are discussed. One approach to laying the foundation for an improved method, using models from the cognitive psychology and behavioral science disciplines, is outlined.