TRANSPORTATION RISK ASSESSMENTS, WHAT CAN WE LEARN FROM 30 YEARS OF PREDICTIONS?

Transportation risk assessments have been routinely performed for the last 30 years. The common purpose of performing such assessments is to show that the impacts of the future shipments will be small and manageable. This paper reviews the assessment methods that have been used and identifies those advancements that have made predicting future impacts more accurate and realistic. The literature review was not limited to the transport of nuclear materials. The literature review showed that many of the limitations in the early assessments have been eliminated through better analysis tools and the availability of better data. The review also identified which assessment tools are the best predictors of transport impacts. When looking at the magnitude of radiological exposures to the general public during normal transport of spent fuel, it was found that it was most important to model the exposures to those people who were most likely to come in close proximity to the spent fuel cask during transport. The models used to evaluate the risk of severe accidents were also evaluated to identify the sources of uncertainty and those parameters that most influence the overall severe accident risk. Since the reported accident risk has been typically several orders of magnitude lower than other impacts, the focus of shipment campaigns should be on ensuring that the predicted low accident risks are realized in practice. This paper clearly shows the value of looking introspectively at the way transport risk assessments are performed. Such efforts identify the uncertainty in current predictions and where efforts should be focused so transport risks can be reduced.