An Overview of the IAEA Safety Series on Procedures for Evaluating the Reliability of Predictions Made by Environmental Transfer Models

The International Atomic Energy Agency (IAEA) is preparing a Safety Series publication on practical approaches for evaluating the reliability of predictions made by environmental radiological assessment models. This IAEA document discusses factors that affect the reliability of model predictions and describes methods for quantifying uncertainty. Emphasis is placed on distinguishing between: (1) uncertainty due to stochastic variability and (2) uncertainty due to lack of knowledge. The document states that the best method for evaluating the accuracy in model predictions is the process of testing against data sets that are independent from those used to develop the model (model validation). For situations in which validation results are not available, analytical and numerical methods are presented for propagating the uncertainty in model parameters into a quantitative statement of uncertainty about the model prediction (parameter uncertainty analysis). The strengths and weaknesses of model intercomparison exercises are also discussed. It is recognized that quantitative statements about the reliability of model predictions must rely upon the use of expert judgment when models are applied to situations that are different from those under which they have been tested.