The discipline of external-initiator PRA analysis is relatively less mature and less reliable than the corresponding internal-initiators PRA analysis. These relative weaknesses have made many decision-makers, in both industry and the NRCuctant to use external-initiator PRA results. The external-initiator analyses have been considered too uncertain, or too conservative, or supported by too little solid data to be of much use. Although this picture has recently begun to change, there is a need to evaluate the extent to which each category of external-initiators PRA methodology, at its current state-of-the art level, produces reliable and useful results and insights, in order to assist decision-makers in understanding both the benefits and the limitations of external-initiator PRA. The proposed project would undertake just such an evaluation. The objective will be, for each external-initiator category separately, to evaluate the reliability and usefulness of the insights available. Specially, the evaluation will address whether the results and insights emerging from current analyses are reliable and useful, and why--and if not, why not. The five initiator categories to be studied are earthquakes, internal fires, external flooding, high winds, and transportation accidents.
