The importance of the urban environment for accident consequences

Accident consequence models are finding increasing use for estimating the risk presented by nuclear installations and providing inputs into decisions on risk acceptability, siting, emergency planning and alternative design options. Their use in this context has implications for the reliability and precision of the model predictions and much effort has been directed in recent years towards quantification of the uncertainties and their reduction where practicable. One of the most important and perhaps least certain parts of accident consequence assessments is the prediction of external radiation from radioactive materials deposited from the atmosphere onto the ground and other surfaces, particularly in urban areas. The potential importance of this exposure pathway for determining the off-site health and economic impacts of an accident are reviewed. The significant parameters influencing this exposure are discussed with particular reference to their uncertainty. (author)