Distributions of risk in exposed groups from routine releases of radionuclides to the environment

This report examines the distribution of risk to members of exposed groups from routine discharges of radionuclides to the environment, by considering the influence on the estimated risk of variability and uncertainty in the parameters in the calculation. Risks, and the doses on which they are based, are presented for two sites, Sellafield and Sizewell, but the calculations are not intended to represent the actual doses or risks to the current critical groups at these locations; it is assumed that that discharges have been made for fifty years at the authorisation limits, and no account is taken of historical accumulations in the environment. The ratio of the 5th to 95th percentiles of dose received by the exposed groups for both sites is typically 3 or 4. The spread in risk across the exposed groups considered has been estimated to be typically an order of magnitude or more. The greatest single contributor to the spread of risk in an exposed group is the risk per unit dose. Estimates of risk to the exposed population do not form part of the authorisation process, although it is possible that in the future risk could be adopted as a common measure to compare the impact of radiological and non-radiological hazards. The results obtained here indicate that, on the basis of current knowledge, the use of risk estimates for radiological exposures in a comparative assessment with other sources of risk needs to be approached with caution. (author)